[PR] fix: await in-flight completion on partner termination in SinkRef [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin opened a new pull request, #3016:
URL: https://github.com/apache/pekko/pull/3016

   ## Motivation
   
   `StreamRefsSpec` *"pass cancellation upstream across remoting before elements has been emitted"* is flaky (#610, upstream akka#30844).
   
   When the consuming `SourceRef` cancels gracefully **before any element**, it sends a `RemoteStreamCompleted` to the origin `SinkRef` and then terminates. On transports such as Artery, system messages (the consumer's `Terminated` / deathwatch) travel on a **dedicated lane** and can overtake the ordinary-lane `RemoteStreamCompleted`. The `SinkRef` then observed `Terminated` first and, with no completion recorded yet, immediately failed with `RemoteStreamRefActorTerminatedException` ("message loss may have happened") — so the origin's `watchTermination` yielded `Failure` instead of `Done`.
   
   The `SinkRef` already guards its *own* termination against this lane race (`finishedWithAwaitingPartnerTermination` + `setKeepGoing`), and the `SourceRef` already waits a `finalTerminationSignalDeadline` grace period when *its* partner terminates (`SourceRefImpl` `TerminationDeadlineTimerKey`). The **symmetric** case on the `SinkRef` side was missing.
   
   ## Modification
   
   When the `SinkRef` observes its partner `Terminated` with no recorded completion/failure, schedule a `finalTerminationSignalDeadline` grace timer instead of failing immediately. If the in-flight `RemoteStreamCompleted` / `RemoteStreamFailure` arrives within the deadline, it completes/fails cleanly via the existing handlers; otherwise the timer fires and message loss is declared as before. The change is confined to the `case _ =>` branch (partner terminated before any completion) — the `Some(Success)` / `Some(Failure)` branches are unchanged.
   
   Removed the corresponding `// FIXME akka#30844` from the test.
   
   ## Result
   
   ```
   [info] Tests: succeeded 24, failed 0   (full StreamRefsSpec)
   cancellation cases: 5/5 on repeat
   stream/mimaReportBinaryIssues: [success] no binary issues
   ```
   
   ## Tests
   
   `stream-tests/testOnly org.apache.pekko.stream.scaladsl.StreamRefsSpec` — 24 pass; cancellation subset 5/5 on repeat. `scalafmt` run; `stream/mimaReportBinaryIssues` clean. Change is internal to `SinkRefStageImpl`.
   
   ## References
   
   Fixes #610


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Re: [PR] fix: await in-flight completion on partner termination in SinkRef [pekko]

["He-Pin (via GitHub)" <gi...@apache.org>]

He-Pin merged PR #3016:
URL: https://github.com/apache/pekko/pull/3016


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