RFR: 8337511: Implement JEP 404: Generational Shenandoah (Experimental) [v7]

[William Kemper]

On Mon, 25 Nov 2024 18:22:09 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> I'll make some adjustments here. Note that `OLD_MARKING` also implies (and sets) `MARKING`, and - unlike `YOUNG_MARKING` - is not exclusive with `EVACUTION` and `UPDATEREFS`. Perhaps an explanatory comment is the best option here?
>
> Thing is, the description for `MARKING` says "marking is in progress" (for any mode), while `YOUNG_MARKING` says that it is only true for yougn marking. So for a casual reader, checking for `YOUNG_MARKING` in non-generational code looks weird. I don't know the best way out of this, really. I think this is the only place when we check `YOUNG_MARKING` for non-gen mode? If so, we should probably fix it right here?

Something like this maybe: https://bugs.openjdk.org/browse/JDK-8344985?

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PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1857241797