RFR: 8322503: Shenandoah: Clarify gc state usage [v3]

[Guoxiong Li]

On Thu, 21 Dec 2023 00:25:09 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> This is a follow up to https://github.com/openjdk/jdk/pull/17112.
>
> William Kemper has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'openjdk/master' into sync-gc-state-followup
>  - Add comments to gc state methods
>  - Rename gc state methods for clarity, assert that only java threads use thread local copy of gc state

Looks good.

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Marked as reviewed by gli (Committer).

PR Review: https://git.openjdk.org/jdk/pull/17163#pullrequestreview-1798050576