RFR: 8351091: Shenandoah: global marking context completeness is not accurately maintained [v4]

[Y. Srinivas Ramakrishna]

On Fri, 7 Mar 2025 01:02:29 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> Good point. I don't see any reason promotions should be verboten in global cycles. cc @earthling-amzn ?
>> 
>> If that is indeed the case, a clean separation and maintenance of completeness of marking for global generation, and use of `_heap->gc_generation()` would make sense to me.
>
> Thanks for the confirmation, I added assert as below since it gc_generation could be global :
> 
> 
> assert(!_heap->gc_generation()->is_old(), "Sanity check");

The assert may be fine, but the treatment of completeness of the marking context seems very brittle to me and apt to cause problems in the future. I would prefer a cleaner separation of these. May be we can sync up separately to discuss this along with @earthling-amzn .

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PR Review Comment: https://git.openjdk.org/jdk/pull/23886#discussion_r1984257756