ResolvedMethodName::vmholder unused?

[Vladimir Ivanov]

> Where does the GC tracks the vmholder? I did a grep of 'vmholder' in all 
> the source code and I can't find anything.

There's a notion of injected fields in HotSpot which aren't present in 
class declaration, but present in the class at runtime (for details see 
JavaClasses::get_injected() called from ClassFileParser::parse_fields()).

vmholder is an object field injected into ResolvedMethodName class. It's 
an ordinary object field, so there's no additional GC support needed to 
support it.

Best regards,
Vladimir Ivanov

> 
> Thanks
> 
> - Ioi
> 
> 
> On 5/7/18 5:45 PM, Vladimir Ivanov wrote:
>> Ioi,
>>
>> Though the field is never accessed directly, 
>> ResolvedMethodName::vmholder is still tracked by GC and keeps the 
>> metadata it accompanies (RMN::vmtarget) alive until RMN is reachable.
>>
>> Best regards,
>> Vladimir Ivanov
>>
>> On 5/7/18 17:29, Ioi Lam wrote:
>>> I don't see anywhere in HotSpot that uses 
>>> java_lang_invoke_ResolvedMethodName::_vmholder_offset, which is 
>>> declared here:
>>>
>>> http://hg.openjdk.java.net/jdk/jdk/file/7444101401b2/src/hotspot/share/classfile/javaClasses.hpp#l1057 
>>>
>>> http://hg.openjdk.java.net/jdk/jdk/file/9608f7f41c4e/src/java.base/share/classes/java/lang/invoke/MemberName.java#l75 
>>>
>>>
>>> I tried commenting out the initialization of this field and was able 
>>> to run a simple Lambda test.
>>>
>>> diff -r 9255cb73f048 src/hotspot/share/classfile/javaClasses.cpp
>>> --- a/src/hotspot/share/classfile/javaClasses.cpp    Mon May 07 
>>> 15:29:31 2018 -0700
>>> +++ b/src/hotspot/share/classfile/javaClasses.cpp    Mon May 07 
>>> 17:27:27 2018 -0700
>>> @@ -3808,7 +3808,7 @@
>>>       // Add a reference to the loader (actually mirror because 
>>> anonymous classes will not have
>>>       // distinct loaders) to ensure the metadata is kept alive.
>>>       // This mirror may be different than the one in clazz field.
>>> -    new_resolved_method->obj_field_put(_vmholder_offset, 
>>> m->method_holder()->java_mirror());
>>> +    //new_resolved_method->obj_field_put(_vmholder_offset, 
>>> m->method_holder()->java_mirror());
>>>       resolved_method = 
>>> ResolvedMethodTable::add_method(Handle(THREAD, new_resolved_method));
>>>     }
>>>
>>>
>>> Any plans to use vmholder in the future? Or, is this used by any 
>>> non-HotSpot VM?
>>>
>>> If no one uses it, I'll file an RFE to remove it, so we can save a 
>>> pointer per MemberName.
>>>
>>> Thanks
>>> - Ioi
>>>
>>>
>>>
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>