RFR: 8377179: Improve and document racy use of start/end in ThreadLocalAllocBuffer [v2]

[Thomas Schatzl]

> Hi all,
> 
>   please review this change that tries to document and streamline the racy use of `ThreadLocalAllocBuffer` internals.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  * ayang review

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/29573/files
  - new: https://git.openjdk.org/jdk/pull/29573/files/d229bddb..723233c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29573&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29573&range=00-01

  Stats: 10 lines in 3 files changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/29573.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29573/head:pull/29573

PR: https://git.openjdk.org/jdk/pull/29573