RFR: 8271880: Tighten condition for excluding regions from collecting cards with cross-references [v11]

[Thomas Schatzl]

On Mon, 20 Sep 2021 12:12:36 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request with a new target base due to a merge or a rebase.
>
> src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp line 116:
> 
>> 114:   if (!dest_attr.is_in_cset()) {
>> 115:     enqueue_card_if_tracked(dest_attr, p, obj);
>> 116:   }
> 
> If I understand this correctly, the only time `dest_attr.is_in_cset() == true` is when `obj` is in a region that failed evacuation, right? To make this even more obvious could we add an else-statement with an assert that this is the case?

This is unfortunately not possible due to races (I tried :)) - one thread may set the flag, another one in the meanwhile already fail again an object in the region, and the evacuation-failed flag not yet visible to this thread.

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PR: https://git.openjdk.java.net/jdk/pull/5037