[11u] RFR 8267561: Shenandoah: Reference processing not properly setup for outside of cycle degenerated GC

[Roman Kennke]

Hi Zhengyu,

The fix looks good.

Is sh/jdk8 affected by this? If so, please mark the bug accordingly (and 
handle the backport if you can).

Thanks,
Roman

> Alibaba reported that Shenandoah outside-of-cycle degenerated GC slowly 
> leak, please see CR for details.
> 
> The cause is that reference processing not setup properly during 
> outside-of-cycle degenerated GC.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8267561/webrev.00/
> 
> Test:
>   hotspot_gc_shenandoah
>   specJVM Debery with configuration reported in CR.
> 
> Thanks,
> 
> -Zhengyu
>