Support IAsyncDisposable

Is your feature request related to a problem? Please describe.

I implement IDisposable in some components to interop with JS, to clean up resources on the JS end. Blazor calls Dispose() on my component as appropriate.

However, this requires using IJSInProcessRuntime to get synchronous JS invocations.

Describe the solution you’d like

If the component implements IAsyncDisposable, Blazor should call (await) DisposeAsync.

[javiercn]

Done in https://github.com/dotnet/aspnetcore/commit/763ccb21b53f281fdb0ae4c894d9040b7b6223a3

[javiercn]

Async disposable support for Blazor

Currently we only support disposing components synchronously. For disposable components there are several design decissions that we’ve made along the way:

• Within a render batch we process the disposed child components for a given component as a bundle, and produce a list of errors each component we process.
• We don’t however, stop the render batch from running. Instead we simply notify the error and let the renderer deal with it within its handle error implementation.
  • RemoteRenderer will terminate the circuit.
  • WebAssemblyRenderer will log the error to the console.
• A component being disposed can trigger a render somewhere else due to some notification during disposal, for example.

All these behaviors happen synchronously, so that means that a render batch only finishes rendering after all the components have been disposed and there are no more renders to process.

Supporting async disposal brings in several questions:

• Do we wait for disposed child components within a given component render to finish disposing before continuing the work?
• Do we wait to send UI updates until all components have successfully been disposed asynchronously?
• Do we trigger new render batches after each component has completed disposing or do we wait until all of the components disposed in a previous batch have finished disposing?

Overview of the design

• We want disposal to behave in a similar way as event handlers and lifecycle methods.
• If as part of disposing an async disposable component a render is triggered within the syncrhonous piece, that render belongs in the same render batch being currently processed.
• Otherwise, it belongs in a separate render batch.
• Synchronous exceptions within async disposables are reported right away.
• Asynchronous exceptions are reported once the task completes.
• We report all the asynchronous disposal errors for a single render batch at the same time.
  • This simplifies processing, but we can also group them by component instead.
  • That said, synchronous errors will be reported before asynchronous errors are so as to not wait for them to complete.