RFR: 8332851: Shenandoah: Update refs iterator does not need to be a member of ShenandoahHeap

[William Kemper]

On Fri, 24 May 2024 02:05:07 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> The iterator is used outside of Shenandoah heap to support an assert, and must be 'reset' for correctness. These iterators are typically used as a local variable, and we can do that with this iterator as well to simplify the code.
>
> src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 2230:
> 
>> 2228:     workers()->run_task(&task);
>> 2229:   }
>> 2230:   assert(cancelled_gc() || !update_refs_iterator.has_next(), "Should have finished update references");
> 
> Help me out here... Can a degenerate GC never pick up in the midst of an update_refs phase, continuing work left from the point of interruption without having to start from scratch?

Yes! It can! Good catch! I'll abandon this PR and fix up `shenandoah:master`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19376#discussion_r1613588878