RFR: 8350649: Class unloading accesses/resurrects dead Java mirror after JDK-8346567 [v4]

[Aleksey Shipilev]

On Tue, 25 Feb 2025 20:13:36 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> Was there a reproducer that can be added with this change? I assume ZGC could have the same sort of problem.

Existing `jdk/jfr` tests fail with Shenandoah reliably (see bug for example invocation), so I felt no need for a new regression test. [JDK-8337978](https://bugs.openjdk.org/browse/JDK-8337978) also helps us to verify we touch the valid Java mirror. There is a larger reproducer in [JDK-8350580](https://bugs.openjdk.org/browse/JDK-8350580), but I am still not 100% sure there are no other bugs it triggers. Once I am sure, I'll add some form of that as regression test.

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PR Comment: https://git.openjdk.org/jdk/pull/23775#issuecomment-2683190245