RFR (M) 8198313: Wrap holder object for ClassLoaderData in a WeakHandle

[coleen.phillimore at oracle.com]

I had an extensive conversation offline with Stefan, Robbin and Kim and 
have reworked this change to walk the CLDG weak roots with the 
SystemDictionary.  Also, I moved the WeakHandle holder creation into the 
ClassLoaderData constructor, and made WeakHandle a template class so 
that multiple weak roots are supported.

open webrev at http://cr.openjdk.java.net/~coleenp/8198313.04/webrev

This passes tier1-5 tests on linux-x64 and windows-x64.  I've also done 
another performance test aka. dev-submit with no significant difference.

The additional change to make _class_loader oop into an OopHandle or 
otherwise remove from ClassLoaderData will be done as a separate change 
because it breaks JFR.

Thanks,
Coleen

On 4/2/18 3:22 PM, coleen.phillimore at oracle.com wrote:
>
>
> On 3/31/18 2:40 PM, Kim Barrett wrote:
>>> On Mar 30, 2018, at 1:53 PM, coleen.phillimore at oracle.com wrote:
>>>
>>>
>>> I have an incremental and full .02 version with the changes 
>>> discussed here.
>>>
>>> open webrev at 
>>> http://cr.openjdk.java.net/~coleenp/8198313.02.incr/webrev
>>> open webrev at http://cr.openjdk.java.net/~coleenp/8198313.02/webrev
>>>
>>> These have been retested on x86, all hotspot jtreg tests.
>>> thanks,
>>> Coleen
>> Looks good.
>>
>> In InstanceKlass::klass_holder_phantom, the klass_ prefix seems
>> unnecessary. I don't need a new webrev if you decide to change the
>> name.
>
> Since it's pre-existing, I don't think I'll address it with this change.
> Thank you for the review.
> Coleen
>