RFR: 8231269: CompileTask::is_unloaded is slow due to JNIHandles type checks [v6]

[Aleksey Shipilev]

On Mon, 28 Apr 2025 18:48:47 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>>> I agree is_permanent_class_loader_data() captures the intent better. Let me see if it fits well here.
>> 
>> Ah wait, it does not. We need to hold on to something that blocks the unloading. Just checking `is_permanent_class_loader_data()` does not get us there. We would need to ask for some holder for it. For the reasons above, `method->method_holder()->klass_holder()` works for non-strong hidden classes as well.
>> 
>> This is also why current mainline code works -- it captures the same thing.
>
> Ok, thanks for checking! Good to know there's no existing bug.
> 
> What I had in mind is as follows:
> 
> InstanceKlass* holder = method->method_holder();
> if (holder->class_loader_data()->is_permanent_class_loader_data()) {
>   return nullptr; // method holder class can't be unloaded
> } else {
>   // Normal class, return the holder that would block unloading.
>   // This would be either classloader oop for non-hidden classes,
>   // or Java mirror oop for hidden classes.
>   assert(holder->klass_holder() != nullptr, "");
>   return holder->klass_holder();
> }
> 
> 
> IMO it makes the check more precise and, at the same time, communicates the intent better. What do you think?

Yes, OK, let's do a variant of that. Committed. I'll re-run test to see if there are any surprises about these asserts.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24018#discussion_r2065897750