Semantics of CollectedHeap::requires_barriers()

[Roman Kennke]

>> However, we might need barriers when copying frames out of the stack chunk (e.g. when thawing frames), because then we'd be loading from oop locations. Is this taken care of already somehow?
> 
> If you need barriers when thawing, then requires_barriers must return false, and then it’s taken care of.

Can you explain to me how that is supposed to work? If I understand it 
correctly, the frozen frame can contain any number of oops. When copying 
back the chunk into the stack, the GC must ensure:
1. That it copies back the correct copy of StackChunk (this might not 
actually be very relevant because the StackChunk is immutable, and thus 
both from-space and to-space copy should be equivalent).
2. More importantly, it must update/heal all oops in the chunk, 
otherwise it violates the strong to-space variant.

How and where is this achieved?

I am asking this, because I still see a failing Fuzz.java test:

http://cr.openjdk.java.net/~rkennke/hs_err_pid623629.log

and I suspect that thawing is not working correctly.

I would expect some sort of GC interface to achieve the above points, 
and conceptually it seems very similar to clone-barriers. But I don't 
see any of this, except NativeAccess<>::oop_load() calls, which 
definitely cannot achieve the desired effect. Or maybe no other GC has 
required such treatment yet, and therefore that's missing?

Roman