RFR: 8319671 GenShen: Old marking may encounter invalid pointers in SATB buffers

[Y. Srinivas Ramakrishna]

On Wed, 8 Nov 2023 01:05:24 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Weak handles which are null'd out after final marking of young, but during marking of old, will have their original referent placed into a SATB buffer. These entries need to be purged before old marking resumes. In the case of abbreviated young cycles, these entries would not be purged.

This seems safe, but we should separately explore as a follow-up a more discriminatory SATB barrier for old vs young marking so a to avoid these wrinkles and the extra work.

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Marked as reviewed by ysr (Committer).

PR Review: https://git.openjdk.org/shenandoah/pull/353#pullrequestreview-1719406785