Does openjdk8u need pre-barrier for jweak?

[Aleksey Shipilev]

Hi Liu,

Yes, I am committer in 8u. But this would require approval from current 8u maintainers. The
maintainers for jdk8u project would normally look at what GC devs said in patch review for
8u-specific patch. So, any patch to G1 in 8u should be RFR'ed on this list (hotspot-gc-dev@) first,
to check with G1 folks that is a proper way to go.

G1 and Shenandoah are definitely affected. I am not sure CMS has this problem: IIRC, remark is
supposed to find live-but-disconnected objects like these.

-Aleksey

On 08/15/2018 06:42 PM, Liu, Xin wrote:
> Agree. I will try to use the similar idea in G1. Aleksey, are you committer of JDK8u? I need to find a sponsor. 
> IMHO, all concurrent GCs have this race condition, right?  Shall we fix CMS? 
> 
> Thanks,
> --lx
> 
> On 8/15/18, 12:50 AM, "Aleksey Shipilev" <shade at redhat.com> wrote:
> 
>     Hi Kim,
>     
>     On 08/15/2018 07:01 AM, Kim Barrett wrote:
>     > However, I think there might be a much simpler solution that retains
>     > at least some clearing of jweaks.  Change the initial mark pause to
>     > always scan and mark the JNI weak globals too, just as the normal JNI
>     > globals are marked.  Leave process_phaseJNI alone (i.e. don't use
>     > Shenandoah's patch.)
>     
>     That is actually a much saner idea for Shenandoah as well, thanks! Should have thought about it at
>     the time. We have moved the workaround block to root processor, which can also distinguish between
>     root processing for concurrent mark and last-ditch STW Full GC:
>       http://mail.openjdk.java.net/pipermail/shenandoah-dev/2018-August/007094.html
>     
>     I think/agree we can apply similar workaround to G1, and move on.
>     
>     -Aleksey
>     
>     
>     
> 


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