Fix shutdown panics by separating completer context#401
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This failing test case exposes the issue in #400 100% of the time, which is caused by the `stopProducers()` call not actually waiting until the producers are fully shut down before proceeding with the remaining shutdown.
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Back in #258 / 702d5b2, the batch completer was added to improve throughput. As part of that refactor, it was turned into a startstop service that took a context on start. We took the care to ensure that the context provided to the completer was _not_ the `fetchCtx` (cancelled on `Stop()`) but instead was the raw user-provided `ctx`, specifically to make sure the completer could finish its work even after fetches were stopped. This worked well if the whole shutdown process was done with `Stop` / `StopAndCancel`, but it did not work if the user-provided context was itself cancelled outside of River. In that scenario, the completer would immediately begin shutting down upon cancellation, even without waiting for producers to finish sending it any final jobs that needed to be recorded. This went unnoticed until #379 / 0e57338 turned this scenario into a panic instead of a silent misbehavior, which is what was encountered in #400. To fix this situation, we need to use Go 1.21's new `context.WithoutCancel` API to fork the user-provided context so that we maintain whatever else is stored in there (i.e. so anything used by slog is still available) but we do not cancel this completer's context _ever_. The completer will manage its own shutdown when its `Stop()` is called as part of all of the other client services being stopped in parallel.
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could this have been causing stuck jobs on graceful shutdown? |
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@elee1766 I believe so, we should add that to the changelog. The core issue is the completer (marks completed jobs in the db) wasn’t properly waiting for jobs to finish executing due to a refactor. So I think it could have resulted in some jobs not being marked as finished when they had in fact executed and returned. |
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Back in #258 / 702d5b2, the batch completer was added to improve
throughput. As part of that refactor, it was turned into a startstop
service that took a context on start. We took the care to ensure that
the context provided to the completer was not the
fetchCtx(cancelled on
Stop()) but instead was the raw user-providedctx,specifically to make sure the completer could finish its work even after
fetches were stopped.
This worked well if the whole shutdown process was done with
Stop/StopAndCancel, but it did not work if the user-provided context wasitself cancelled outside of River. In that scenario, the completer would
immediately begin shutting down upon cancellation, even without waiting
for producers to finish sending it any final jobs that needed to be
recorded. This went unnoticed until #379 / 0e57338 turned this scenario
into a panic instead of a silent misbehavior, which is what was
encountered in #400.
To fix this situation, we need to use Go 1.21's new
context.WithoutCancelAPI to fork the user-provided context so that wemaintain whatever else is stored in there (i.e. so anything used by slog
is still available) but we do not cancel this completer's context
ever. The completer will manage its own shutdown when its
Stop()iscalled as part of all of the other client services being stopped in
parallel.
Fixes #400.