Preview: Concurrent JNIWeakHandles processing

[Stefan Karlsson]

Hi all,

Kim recently pushed a patch to jdk/hs, which contains the new OopStorage 
class. This class is a container for oops, and helps separating GC 
scanning/clearing from Runtime data structure cleaning/unlinking. The 
OopStorage also provides the functionallity to scan/clear the oop*s 
concurrently.

The container of the JNIWeakHandles has been changed to the OopStorage, 
but the clearing is currently done during pauses. The following patch 
adds concurrent clearing to ZGC. The patch moves the clearing out from 
the "mark end" pause into the "concurrent weak processing" phase after 
mark end.

I want to do further testing before this gets pushed, but here's the 
current patch:

http://cr.openjdk.java.net/~stefank/zgc/zConcurrentJNIWeakHandles/webrev.01/

Thanks,
StefanK