Add an event that is fired after all dependencies are ready

[AndriySvyryd]

Is there an existing issue for this?

• I have searched the existing issues

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

The problem is that BeforeStartEvent handlers are evaluated sequentially. So, if the BeforeStartEvent handler for the API app is waiting for a resource to become ready and it in turn needs BeforeStartEvent handlers to finish running it becomes a deadlock.

See #13481 (comment)

Describe the solution you'd like

Add an event that runs after all the dependencies of a resource are in the ready state and the resource is actually ready to start.

Additional context

No response

[karolz-ms]

@AndriySvyryd can you elaborate what you mean by "BeforeStartedEvent handlers are evaluated SEQUENTIALLY" (emphasis mine), and why it is a problem?

Also, this does not seem to be an issue specific to integrations, but more of a general Aspire app model issue?

[AndriySvyryd]

@AndriySvyryd can you elaborate what you mean by "BeforeStartedEvent handlers are evaluated SEQUENTIALLY" (emphasis mine), and why it is a problem?

Maybe that wasn't the correct word. What I mean is that the next registered handler only runs after the previous completed. There are two problems with this. There's a deadlock if they happen to be ordered in a way where the previous one depends on a resource being ready that can only get to that state after the next handler runs. And a more common case is when the resource cannot run until all BeforeStartedEvent handlers are finished, so even a single handler waiting on a resource with dependencies causes a deadlock.

Also, this does not seem to be an issue specific to integrations, but more of a general Aspire app model issue?

Sure, it just seems to mostly impact integrations.

[karolz-ms]

OK I understand now, thanks, and I believe this will be solved by fixing #14952