RFR (S): 8202018: Move card table clear before enqueuing pending references

[Stefan Johansson]

Looks good,
StefanJ

On 2018-04-19 20:48, Thomas Schatzl wrote:
> Hi all,
> 
>    can I have reviews for this small change in preparation of "JDK-
> 8202017: Merge Reference Enqueuing phase with phase 3 of Reference
> processing"?
> 
> So to be able to merge reference enqueuing with reference processing,
> we need to make sure that the card marks of reference enqueuing are not
> overwritten by card table clearing.
> 
> Card table clearing wipes data that the previous scan rs and update rs
> phases have written to the card table to do duplicate card in
> remembered sets detection.
> Investigation of the code shows that since both scan rs and update rs
> have already finished at the point of reference processing, we can
> simply do the card table clearing before reference processing too -
> otherwise it would at worst hide an existing bug as only scan rs and
> update rs actually add to the list of regions' card tables to clear.
> 
> Looking at the code, doing the change, and testing all showed that this
> seems fine.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8202018
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8202018/webrev/
> Testing:
> hs-tier1-4 with and without VerifyCTCleanup enabled (as it is a develop
> flag and would give issues with the product, I temporarily
> unconditionally enabled it via code)
> 
> Thanks,
>    Thomas
>