RFR: 8367142: Simplify java mirror handling in JNI methods

[Ioi Lam]

On Tue, 9 Sep 2025 05:58:32 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Sorry but I think this PR is trying to do too many things at once.
> 
> It is pushing JNI resolving inside internal JVM methods, which I think is a bad thing - we resolve JNI references at the boundary to get the oop that the VM wants to work with. Internal APIs should be oblivious to jobject and friends IMO. Also there may be times that the JNI/JVM method needs get the oop itself before extracting the klass.

There are 92 header files that have the word `jobject` in them. There are 71 cpp/hpp files with the word `JNIHandles::resolve` in them. So I am not sure if we really have that separation anymore.

There are 54 cases where we call `as_Klass(JNIHandles::resolve_non_null(x))`, so I think it would be nice to have a way to write less code.

> You are converting klass to instanceKlass where it has to be instanceKlass e.g. with redefinition. This is a good thing, but it is a very distinct thing that deserves its own cleanup (as per previous changes in that area).


I can move the considering_redefinition changes in a follow-up PR.

> You are defining a helper `java_lang_Class::as_InstanceKlass` to internalize the cast - this is fine but again a simple cleanup that would be better standalone IMO.
> 
> It is also not clear that JVM/JNI API's are properly checking that the incoming jobject is in fact a class of the right kind (ie not an array class object).

I am just converting


InstanceKlass* ik = InstanceKlass::cast(as_Klass(mirror));


to 


InstanceKlass* ik = as_InstanceKlass(mirror);


The code already assumes that it has an InstanceKlass, and I am not changing that.

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PR Comment: https://git.openjdk.org/jdk/pull/27158#issuecomment-3269072414