MartijnVisser opened a new pull request, #29039:
URL: https://github.com/apache/flink/pull/29039
## What is the purpose of the change
Resolves FLINK-40503 by documenting when `withIdleness` actually takes
effect. The `WatermarksWithIdleness` countdown is anchored at the first quiet
periodic probe rather than at the last record, and the strict `>` comparison
only fires at the next probe after the timeout is exceeded — so idleness is
detected between idleTimeout and idleTimeout plus three watermark intervals
after the last record (the worst case is attained when the timeout is an exact
multiple of the auto-watermark interval). The javadoc previously implied
detection at idleTimeout. The timing itself is intentionally left unchanged:
silently changing detection timing in this area has a regression track record
(cf. the FLIP-471 follow-ups).
## Brief change log
- Clarified the `WatermarkStrategy#withIdleness` javadoc and the
`WatermarksWithIdleness` class doc with the precise detection-timing contract.
- Added an equivalent paragraph to the "Dealing With Idle Sources" section
of the event-time documentation (English page; updating the Chinese translation
is a follow-up).
- Added `WatermarksWithIdlenessTimeoutTest`, pinning the documented timing
deterministically with a manual clock (timeout 10ms, probes every 5ms: not idle
at the probes 11ms and 16ms after the last event, idle at the probe 21ms after
it).
## Verifying this change
This change added tests and can be verified as follows:
- New deterministic `WatermarksWithIdlenessTimeoutTest` pins the documented
detection timing.
- Existing `WatermarksWithIdlenessTest` and `WatermarkStrategyTest` pass
unchanged; no existing tests were modified.
- Otherwise documentation-only; no behavior change.
## Does this pull request potentially affect one of the following parts:
- Dependencies (does it add or upgrade a dependency): no
- The public API, i.e., is any changed class annotated with
`@Public(Evolving)`: no (javadoc-only changes on
`WatermarkStrategy`/`WatermarksWithIdleness`)
- The serializers: no
- The runtime per-record code paths (performance sensitive): no
- Anything that affects deployment or recovery: JobManager (and its
components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
- The S3 file system connector: no
## Documentation
- Does this pull request introduce a new feature? no
- If yes, how is the feature documented? not applicable (clarifies
existing documentation)
---
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- [X] Yes (please specify the tool below)
Generated-by: Claude Code (Fable 5)
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