RFR: 8295319: pending_cards_at_gc_start doesn't include cards in thread buffers

[Kim Barrett]

On Mon, 31 Oct 2022 08:31:13 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> `calculate_collection_set` -> `finalize_initial_collection_set` -> `finalize_young_part`: `size_t pending_cards = _policy->pending_cards_at_gc_start() + _g1h->hot_card_cache()->num_entries();`
> 
> called before `pre_evacuate_collection_set`
> 
> `flush_dirty_card_logs_and_stats` needs to be called before `calculate_collection_set`

Sigh!  Looks like I got lost while tracking down the callers and call chains.

So the use in `finalize_young_part` is presumably using the pending cards count from the previous
collection, which usually isn't such a bad value that it causes anything goes off the rails, so testing
didn't spot a problem.

I kind of hate some of that code, which has too many non-obvious and unchecked (and not easily
checked) ordering constraints.

Thanks for spotting this.

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PR: https://git.openjdk.org/jdk/pull/10914