Re: convert various variables to atomics

Hi Nathan,

I tested the complete v1 patch series on PostgreSQL 20devel.
The patches applied cleanly, and PostgreSQL built and installed
successfully. The server started without any issues after applying the
patches.
I performed functional testing for the areas affected by the patch
series, including shared invalidation, parallel bitmap heap scan,
parallel WAL state handling, startup process shared state, parallel
sort, SharedFileSet temporary file handling, parallel sequential scan,
and fast-path relation locking. For each patch, I compared the
behavior before and after applying the changes and observed no
functional differences. All tests behaved as expected, and I did not
encounter any crashes, assertion failures, or unexpected behavior.

I also ran the regression test suite using make check. All regression
tests passed successfully, and the generated regression.
Overall, I did not observe any functional regressions during testing.
The patch series looks good from my testing.

Thank you for working on this improvement.

Regards,
Solai