RFR(S): G1: assert(da ? referent->is_oop() : referent->is_oop_or_null()) failed: referenceProcessor.cpp:1054

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers to review the changes for this CR? The 
webrev can be found at: http://cr.openjdk.java.net/~johnc/7097053/webrev.0/

Summary:
During RSet scanning the reference processor was discovering a reference 
oop whose referent object failed the is_oop() test in the failing 
assert. It appears that is was being caused by a race between RSet 
updating (which did not perform reference discovery) and RSet scanning 
(which did) and so the reference processor could see a referent object 
that was in the process of being copied. To resolve this issue we have 
decided to not do reference discovery duing RSet scanning.

Testing: The failing test case (with a 1ms delay between object 
forwarding and copying - which increases the frequency of hitting the 
assert almost 3x) on highly threaded SPARC T2 systems; OpenDS on x64.

Thanks,

JohnC