RFR: 8361342: Shenandoah: Evacuation may assert on invalid mirror object after JDK-8340297

[Thomas Stuefe]

On Wed, 9 Jul 2025 15:16:19 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>>> > Only looked at this briefly, but that sounds like what I did here: #21064 -- but forgot to complete it?
>>> 
>>> Yes, it looks like it is! The sequence of events you describe seems to also match [JDK-8340364](https://bugs.openjdk.org/browse/JDK-8340364), which I think we can close as duplicate, as I have not been able to convince even myself is a real bug, not just overzealous verification. So, what do you want to do? I can finish up #21064 and test it with your Metaspace assertion patches, if you want.
>> 
>> Thanks, let me just finish this, I need the closure after burning time on this non-bug :-)
>> 
>> Note that I did not fix up the use of the array mirror klass since I thought it should always be stable. We never redefine array classes. But then it does not hurt either.
>> 
>> I am also preparing a small improvement patch for print_obj, as per our discussion in https://github.com/openjdk/jdk/pull/26117 yesterday, and will put the printing of the mirror klasses there, too.
>
>> Thanks, let me just finish this, I need the closure after burning time on this non-bug :-)
> 
> Sure, OK. Please pick up most of the hunks from https://github.com/openjdk/jdk/pull/21064, including the array mirrors then? I don't see a need to write a full paragraph of text explaining why we need to check for forwarded objects. A simple sentence is enough, and the rest can go into the bug description.

@shipilev ok done

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PR Comment: https://git.openjdk.org/jdk/pull/26187#issuecomment-3055805609