RFR: 8357976: GenShen crash in swap_card_tables: Should be clean

[Xiaolong Peng]

On Tue, 10 Jun 2025 20:14:49 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Degenerated cycles must also clean the `read` card table before swapping it with the `write` card table.

src/hotspot/share/gc/shenandoah/shenandoahDegeneratedGC.cpp line 142:

> 140:         // Clean the read table before swapping it. The end goal here is to have a clean
> 141:         // write table, and to have the read table updated with the previous write table.
> 142:         heap->old_generation()->card_scan()->mark_read_table_as_clean();

Should we clean only when _generation is young, given we swap card tables when _generation is young?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25735#discussion_r2138774860