RFR: 8339725: Concurrent GC crashed due to GetMethodDeclaringClass [v2]

[Coleen Phillimore]

On Mon, 9 Sep 2024 06:04:36 GMT, Liang Mao <lmao at openjdk.org> wrote:

>> Hi,
>> 
>> It's a fix for 8339725. I think getting the oop from Klass::java_mirror() should use a ON_PHANTOM_OOP_REF decorator here which could make sure the oop would be kept alive in concurrent marking and return nullptr while in concurrent reference processing and unloading.
>> 
>> test/hotspot/jtreg/runtime and gc are clean.
>> 
>> Thanks,
>> Liang
>
> Liang Mao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix build error in windows/mac

Holding a mirror in a Handle must keep the CLD alive.  If it has an oop class loader, it will keep a reference to that class loader alive through the vectors field.  If it is a mirror holder CLD, the holder is the mirror itself.  You can only unload the CLD if the CLD::holder is unreachable.  This Handle makes the CLD holder reachable.

Not having this property breaks everything.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/20907#issuecomment-2338470827