RFR: 8352588: GenShen: Enabling JFR asserts when getting GCId [v4]

[Y. Srinivas Ramakrishna]

On Mon, 24 Mar 2025 18:30:23 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   No need to calculate gc_id using gc_count
>
> src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp line 137:
> 
>> 135:       // GC is starting, bump the internal gc count and set GCIdMark
>> 136:       update_gc_count();
>> 137:       GCIdMark gc_id_mark;
> 
> Can we still set the `GCIdMark` with our internal counter? I'd prefer they stay in sync explicitly.

@earthling-amzn : Is your concern that GC count is incremented concurrently by two different callers? If so, I'd have the atomic increment return the pre- or post-increment value as the case may be and have the caller use that in their mark label. (Question: do we have different Id's for young and a concurrent/interrupted old? -- I would imagine so, with the old carrying an older id, and each subsequent young getting a newer id).

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PR Review Comment: https://git.openjdk.org/jdk/pull/24166#discussion_r2011041651