RFR: 8272231 G1: Refactor G1CardSet::get_card_set to return G1CardSetHashTableValue*

[Kim Barrett]

On Tue, 10 Aug 2021 15:11:02 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi all,
> 
> Please review this change to return G1CardSetHashTableValue* from G1CardSet::get_card_set. Consequently, we do not have to use G1CardSet::get_or_add_card_set in instances where we only need to get the table entry (such as in G1CardSet::transfer_cards_in_howl).
> 
> Testing: Tier 1-5.

Changes requested by kbarrett (Reviewer).

src/hotspot/share/gc/g1/g1CardSet.cpp line 195:

> 193: 
> 194:   class G1CardSetHashTableFound : public StackObj {
> 195:     G1CardSetHashTableValue* _value = nullptr;

Non-static data member initializers (http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2008/n2756.htm) have not (yet) been approved for use in HotSpot.  Needs to be initialized in a constructor.

src/hotspot/share/gc/g1/g1CardSet.cpp line 612:

> 610:     Atomic::add(&howling_array->_num_entries, diff, memory_order_relaxed);
> 611: 
> 612:     G1CardSetHashTableValue* table_entry = get_card_set(card_region);

Maybe there should be an assert here that `table_entry` is non-null.

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PR: https://git.openjdk.java.net/jdk/pull/5072