RFR: 8201646: Introduce ReferenceDiscoverer interface

[Per Liden]

On 04/17/2018 02:54 PM, Thomas Schatzl wrote:
> Hi Per,
> 
> On Tue, 2018-04-17 at 14:20 +0200, Per Liden wrote:
>> Introduce ReferenceDiscoverer interface to allow for alternative
>> ReferenceProcessor implementations. The current ReferenceProcessor
>> implementation is built for STW operation, which is undesirable for
>> low latency GCs.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8201646
>> Webrev: http://cr.openjdk.java.net/~pliden/8201646/webrev.0
>>
> 
>    great, I also thought about introducing such an interface, but
> hesitated because of the additional work :)

Thanks for reviewing!

I noticed one thing in my patch. To get the oop type I'm including 
oop.hpp instead of oopsHierarchy.hpp. I'll fix this before pushing.

--- a/src/hotspot/share/gc/shared/referenceDiscoverer.hpp
+++ b/src/hotspot/share/gc/shared/referenceDiscoverer.hpp
@@ -27,7 +27,7 @@

  #include "memory/allocation.hpp"
  #include "memory/referenceType.hpp"
-#include "oops/oop.hpp"
+#include "oops/oopsHierarchy.hpp"

> 
> My question is, did you perform at least some cursory performance
> checking because this adds a virtual call?

I did run specjbb2015 (which uses SoftRefs fairly heavily), 2 iterations 
with and 2 iterations without my patch. No measurable difference in 
pause times.

cheers,
Per

> 
> Looks good otherwise.
> 
> Thanks,
>    Thomas
>