This PR proposes to improve the handling of the fields in `LazyCollections.Mutexes` so that it becomes more evident there are no races. It is also proposed to add a defensive check of `mutexes` so that it is obvious for a reader that the `Unsafe` operation does not operate on `null`. Furthermore, it is proposed to remove the extra `AtomicInteger` object and use an `int` field directly.
--------- - [x] I confirm that I make this contribution in accordance with the [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). ------------- Commit messages: - Improve comments - Add comments and add explicit semantics - Rework how Mutexes works Changes: https://git.openjdk.org/jdk/pull/32070/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=32070&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8389250 Stats: 15 lines in 1 file changed: 7 ins; 1 del; 7 mod Patch: https://git.openjdk.org/jdk/pull/32070.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/32070/head:pull/32070 PR: https://git.openjdk.org/jdk/pull/32070
