clintropolis opened a new pull request #9982:
URL: https://github.com/apache/druid/pull/9982
### Description
This PR makes `Joinable`, `JoinClause`, and `IndexedTable` implement
`Closeable`, so that a future PR can add reference counting for `IndexedTable`
that are backed by a `Segment` described in proposal #9953. `HashJoinSegment`
now wraps a `ReferenceCountingSegment`, allowing both the segment reference
count to be incremented/decremented when used, and also closing the associated
list of `JoinClause` when the references to the segment are released.
`ReferenceCountingSegment` has been refactored to extend a new base type,
`ReferenceCountingClosableObject`, which handles the actual reference counting
part and prepare for `ReferenceCountingIndexedTable` (which does not exist yet).
A new interface, `SegmentReference` has been added to capture a `Segment`
which has references which must be acquired and released:
```
public interface SegmentReference extends Segment
{
Optional<Closer> acquireReferences();
}
```
The contract of the closer is that if the call to
`ReferenceCountingClosableObject#increment` is successful, then a closer will
be present in the `Optional`, which when closed will call
`ReferenceCountingClosableObject#decrement` on any tracked references.
`ReferenceCountingSegment` and `HashJoinSegment` implement this interface, and
`ReferenceCountingSegmentQueryRunner` now operates on this interface instead of
directly using `Segment` and a `ReferenceCounter`.
Finally, I have marked `AbstractSegment` as deprecated, and moved it's only
functionality into a default method on the interface to make working with
`Segment` a bit easier. I have not deleted `AbstractSegment` yet, it's just an
empty husk that we can remove in a future release on the off chance that any
custom extensions are relying on this class.
<hr>
This PR has:
- [ ] been self-reviewed.
- [ ] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
(Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/licenses.yaml)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
<hr>
##### Key changed/added classes in this PR
* `ReferenceCountingSegmentQueryRunner`
* `ReferenceCountingClosableObject`
* `ReferenceCountingSegment`
* `HashJoinSegment`
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