[15] RFR 8238633: JVMTI heap walk should consult GC for marking oops

[Zhengyu Gu]

Hi,

>> So perhaps just adding the NULL check in the barrier for the case 
>> where the markWord ”is_marked” is the sane thing to do, knowing that 
>> the other costs taken in the same path will dominate.
> 
> I have this patch, exactly what you suggested. I will let Aleksey run 
> his numbers.

Aleksey is happy with the solution, as we are able to split compiler 
barrier and runtime barrier. Therefore, I would like to withdraw this CR.

Thanks all of you!

-Zhengyu