RFR: 8138888: Remove ExtendedOopClosure::apply_to_weak_ref_discovered_field

[Kim Barrett]

> On Apr 25, 2017, at 7:41 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
> 
> Hi,
> 
> Please review this change for:
> https://bugs.openjdk.java.net/browse/JDK-8138888
> 
> Webrev:
> http://cr.openjdk.java.net/~sjohanss/8138888/hotspot.00/
> 
> Summary:
> This change builds upon 8138737 which is currently out for review. With that change we now have a more generic mechanism to add special handling for closures when visiting InstanceRefKlasses. With this mechanism we can remove ExtendedOopClosure::apply_to_weak_ref_discovered_field and replace it with a new ReferenceIterationMode which provides the same functionality.
> 
> The RFE in JBS also proposes to remove the functionality of apply_to_weak_ref_discovered_field, but to do this some more analysis is needed. Doing this changes is a step in the direction of making it easier to remove the need for this functionality in future changes.
> 
> Testing:
> * JPRT
> * RBT hs-tier 2+3
> 
> Thanks,
> Stefan

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src/share/vm/oops/instanceRefKlass.inline.hpp

 114 void InstanceRefKlass::oop_oop_iterate_discovered_and_discovery(oop obj, ReferenceType type, OopClosureType* closure, Contains& contains) {
 115   // Explicitly apply closure to the discovered field.
 116   do_discovered<nv, T>(obj, closure, contains);
 117   // Then do normal reference processing with discovery.
 118   oop_oop_iterate_discovery<nv, T>(obj, type, closure, contains);
 119 }

This will apply the closure to the discovered field, and then
(conditionally) log the processing of the reference (at the start of
oop_oop_iterate_discovery).

Also, oop_oop_iterate_fields doesn't have a corresponding log message
at the start.

Maybe the thing to do is to have the on-entry logging in
oop_oop_iterate_ref_processing_specialized, with the message
specialized by the iteration mode.

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