RFR: Add generations to freeset [v5]

[Kelvin Nilsen]

On Thu, 13 Apr 2023 16:10:00 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Remove debug instrumentation
>
> src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp line 69:
> 
>> 67:   inline bool peek_is_mutator_free(size_t idx) const;
>> 68:   inline bool peek_is_collector_free(size_t idx) const;
>> 69:   inline bool peek_is_old_collector_free(size_t idx) const;
> 
> I can imagine needing these during transitions in membership. I am wondering though if the assertion checking can be refactored in such a manner that we don't need these `peek` versions at all. They have a kind of ad-hoc feel to them, as if we were shoe-horning assertion checks in the wrong place(s). See suggestion/comments further above.

I understand.  I'm adding some comments to try to clarify.  (maybe a bigger fix can come later to refactor the implementation of how set membership is represented.)

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/250#discussion_r1170642340