RFR (XL): 8202845: Refactor reference processing for improved parallelism

[Kim Barrett]

> On Jun 12, 2018, at 3:39 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
>> On Jun 12, 2018, at 2:19 PM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:http://cr.openjdk.java.net/~tschatzl/8202845/webrev.1_to_2 (diff)
>> http://cr.openjdk.java.net/~tschatzl/8202845/webrev.2 (full)
> 
> Looks good.

One more thing I just noticed.

src/hotspot/share/gc/shared/referenceProcessor.cpp
 865   log_reflist("Phase2 Soft after", _discoveredSoftRefs, _max_num_queues);
 866   log_reflist("Phase2 Weak after", _discoveredWeakRefs, _max_num_queues);

at the end of process_soft_weak_final_refs.  At this stage, I think
there must be no soft or weak references.  Better to assert that than
log empty sets.

Similarly at the end of process_phantom_refs.

And the same is true for process_final_keep_alive.