RFR: 8322296: Introduce CardWord for word iteration on CardTable

[Thomas Schatzl]

On Mon, 18 Dec 2023 14:15:58 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> Simple adding a new type for card-word in `CardTable` in order to avoid repeating the same logic/typedef in card based collectors.

Lgtm.

I noticed that the parallel gc card scanning does not use the word-based scan. Something for a different CR (if not just reusing the scanning for all collectors in some way).

src/hotspot/share/gc/shared/cardTable.hpp line 43:

> 41:   STATIC_ASSERT(sizeof(CardValue) == 1);
> 42: 
> 43:   using CardWord = uintptr_t;

Not really convinced this is a good name, but I do not have a good alternative either right now.

src/hotspot/share/gc/shared/cardTable.hpp line 75:

> 73:   };
> 74: 
> 75:   static const CardWord clean_card_word = (CardWord)(-1);

I would somewhat (not strongly) prefer if this constant explicitly constructed this value out of `clean_card` values. Or some static assert that the value is as expected.
Maybe this is not worth the effort though.

-------------

Marked as reviewed by tschatzl (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17144#pullrequestreview-1790631152
PR Review Comment: https://git.openjdk.org/jdk/pull/17144#discussion_r1432552215
PR Review Comment: https://git.openjdk.org/jdk/pull/17144#discussion_r1432551332