On Wed, 12 Aug 2026 21:57:07 GMT, Chris Plummer <[email protected]> wrote:
>> Yasumasa Suenaga has updated the pull request incrementally with one
>> additional commit since the last revision:
>>
>> Improve OopField::getOffset
>
> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/oops/OopField.java line
> 64:
>
>> 62: public long getOffset() {
>> 63: long ofs = super.getOffset();
>> 64: if ((inlineKlass != null) || (inlineKlass == null && isFlat())) {
>
> Can you explain a bit how this works. I thought an InstanceKlass that is
> inlineable is marked as such, but that doesn't imply it will actually be
> inlined (flattened) for every field reference. The field referencing the
> inlineable class is marked as "flat" if it is actually flattened. How do we
> end up with (inlineKlass == null && isFlat()) being true? I would think that
> isFlat() being true would imply (inlineKlass != null) being true.
I've added this condition for followup bugs (FlatArray).
In FlatArray, I think we can traverse flattened array oop as following. We need
to pass holder (element) Klass to `OopField`. In `Instance` (`oop`), `OopField`
associates with the field owner, so `isFlat()` can work. OTOH `Inline` in
`FlatArray` is just the value, and we need to instantiate `OopField` directly.
It means we cannot access metadata - it is JDK-8247507.
FlatArrayKlass klass = (FlatArrayKlass)getKlass();
InlineKlass elementKlass = (InlineKlass)klass.getElementKlass();
for (int index = 0; index < length; index++) {
long offset = baseOffset + (index * elementSize);
OopField field = new OopField(new IndexableFieldIdentifier(index),
offset, false, elementKlass);
visitor.doOop(field, false);
}
Hence we need to consider two conditions to detect vaule object:
1. `inlineKlass != null`: for FlatArray: `Klass` is injected in force.
2. `inlineKlass == null && isFlat()`: Flattened field in (normal) oop: we can
access metadata via `isFlat()`.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/32310#discussion_r3771614870
