Allow clearing of cached type infos via explicit method call - Mediator._notificationHandlers

[Ralf1108]

We use MediatR to implement a plugin infrastructure for a table data program.
We defined messages in a plugin interface assembly which is used for each plugin. The plugin can also define their own messages.
Then we load the plugins via AssemblyLoadContext and register all request handlers vi DI and RegisterServicesFromAssembly().
Afterwards we can call the request handlers in the plugins via the IMediatR interface.

The issue is when we want unload the plugin during runtime.
We observed when we used "mediator.Publish" then there will be NotificationHandlerWrapper instances cached in a static field inside MediatR.
The wrappers are created here
and cached here.

The caching of these wrappers when they contain message types from the plugin assemblies prevents them from being unloaded properly.
We used the Visual Studio Memory to verify this:

We did not find a way to clear this cache except using reflection code:

// remove static references from Mediator when used "mediator.Publish"
var fieldInfo = typeof(MediatR.Mediator).GetField("_notificationHandlers", BindingFlags.Static | BindingFlags.NonPublic);
var value = (ConcurrentDictionary<Type, NotificationHandlerWrapper>)fieldInfo.GetValue(null);
value.Clear();

Is it possible to provide an official method to clear cached values inside MediatR?

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