On Fri, 28 Aug 2026 18:33:27 GMT, Dan Heidinga <[email protected]> wrote:
>>> @AlanBateman you are right that heapdump and followrefs tools will not
>>> visit the class after visiting the class loader with this change. They'll
>>> still visit the class loader with the class. I'm still trying to work out
>>> how to describe this change in behavior for these tools and maybe have a
>>> CSR for it. There was only one test left that failed because of this change
>>> - was hoping some hprof test would fail so I could see the effect of that.
>>> I'm still working on this though, but I wanted to publicize the change
>>> first.
>>
>> I worry this is a significant behavior change that will blind some heap
>> analysis tools. As part of "I'm still working on this", would you mind
>> looking into synthesizing these refs so that tools using FollowReferences
>> will follow refs to the loaded classes?
>
>> I worry this is a significant behavior change that will blind some heap
>> analysis tools. As part of "I'm still working on this", would you mind
>> looking into synthesizing these refs so that tools using FollowReferences
>> will follow refs to the loaded classes?
>
> Rather than relying on the ArrayList of Class objects in ClassLoader to
> provide the reference links, can we update the `VM_HeapWalkOperation` used
> by JVMTI FollowReferences to treat ClassLoaders specially?
>
> The `VM_HeapWalkOperation::visit` operation in jvmtiTagMap.cpp can add a case
> for classloaders to iterate them specially:
>
> if (klass->is_class_loader_instance_klass()) {
> return iterate_over_classloader(o);
> }
>
> where `iterate_over_classloader` fetches the ClassLoaderData and then
> iterates over its _klasses?
I don't think we should be changing behaviour here. I think calling
`FollowReferences` from a ClassLoader instance should continue to report all
classes loaded by that loader. This behaviour is too long-standing to just
change it now. As @DanHeidinga suggested we need to update the
`FollowReferences` implementation so that it still returns the loaded classes.
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PR Comment: https://git.openjdk.org/jdk/pull/32519#issuecomment-5503162834
