[jdk20u] RFR: 8307378: Allow collectors to provide specific values for GC notifications' actions

[Paul Hohensee]

On Tue, 9 May 2023 17:13:55 GMT, William Kemper <wkemper at openjdk.org> wrote:

> Unclean backport of JDK-8307378. Merge conflicts were trivial instances of `NULL`  vs `nullptr`.

Lgtm.

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Marked as reviewed by phh (Reviewer).

PR Review: https://git.openjdk.org/jdk20u/pull/75#pullrequestreview-1420813810