fix: Handle error state in Init() with TaskCompletionSource

[askpt]

Signed-off-by: André Silva 2493377+askpt@users.noreply.github.com

This PR

This pull request refactors the initialization and event handling logic in the InProcessResolver to simplify thread management and improve reliability. The main change is replacing the use of CountdownEvent and a background thread with a more modern TaskCompletionSource-based approach for signaling initialization completion.

Initialization and event handling improvements:

• Replaced the use of CountdownEvent and manual thread management in Init() with a TaskCompletionSource<bool> and Task.Run, simplifying the initialization flow and reducing complexity.
• Updated HandleEvents to accept a TaskCompletionSource<bool> instead of a CountdownEvent, and to signal initialization completion by calling TrySetResult(true) when the first event is received or on error. [1] [2] [3]

Notes

This should fix the flaky tests because we were not "signalling" correctly when the exception happens.

[gemini-code-assist]

Summary of Changes

Hello @askpt, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the error handling and initialization process of the InProcessResolver by using TaskCompletionSource to manage asynchronous operations. This ensures that the Init() method completes gracefully, even in error scenarios, and simplifies the synchronization logic.

Highlights

• Error Handling: The Init() method now handles error states by using a TaskCompletionSource to signal completion even when an exception occurs during the event handling, ensuring the provider is marked as 'ready' but in an error state.
• Asynchronous Initialization: Replaced CountdownEvent with TaskCompletionSource for asynchronous initialization in Init(), simplifying the synchronization logic and improving readability.
• Event Handling: Modified the HandleEvents method to use TaskCompletionSource to signal completion, allowing Init() to complete even if there are issues with the event stream.

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[gemini-code-assist]

Code Review

This pull request refactors the initialization logic in InProcessResolver to use TaskCompletionSource instead of CountdownEvent, which is a good modernization. It also aims to fix a hang in Init() by handling RpcException. My review identifies a critical flaw in the error handling strategy: other types of exceptions are not handled, which can still lead to Init() hanging. I've provided a comprehensive suggestion to make the error handling more robust, ensuring that all exceptions are managed correctly and that the provider initialization is resilient.

[chrfwow]

I wonder if we should set the state before or after we emitted the error event.
I am afraid that we might consider the provider to be in a non error state in the time from tcs.TrySetResult(true); to ProviderEvent?.Invoke(this, flagdEvent);, but I am also afraid to deadlock something (we had a roughly similar situation in the java flagd, which did result in a deadlock), because the event is not getting properly propagated

[askpt]

Good point and thank you for your insight coming from Java experience. Fixed with 7489afc