RFR: 8375974: G1: Convert G1FullCollector to use Atomic<T>

[Thomas Schatzl]

On Wed, 21 Jan 2026 17:58:47 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> Idk. I think it is just about the `_compaction_tops` being aligned, i.e. can be atomically read. Also to just indicate that the array is accessed concurrently.
>> 
>> I can remove these completely if wanted.
>
> There wasn't any alignment futzing in the old code, so I don't think that's it.
> I've not looked to see if it can be removed; I was asking if you knew the answer.

The compaction_tops are written in one phase of full gc, and read in other phases, both in parallel, but the writing is non-overlapping (and reads do not matter).

The only reason I can think of is to indicate that the elements are accessed in parallel.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/29342#discussion_r2713729502