RFR: Move JNI Weak References workaround to Shenandoah-specific root processor

[Zhengyu Gu]

Good to me.

-Zhengyu

On 08/15/2018 03:49 AM, Aleksey Shipilev wrote:
> We have this workaround in 8u:
>    http://hg.openjdk.java.net/shenandoah/jdk8u/hotspot/rev/ba692039a40a
> 
> Kim Barrett suggested a saner approach to it -- which makes the workaround more to the point, allows
> collecting jweaks during Full GC, and avoids bugs in whatever other codepath in RP that polls jweak
> liveness:
>    http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2018-August/022931.html
> 
> This patch implements that suggestion for Shenandoah:
>    http://cr.openjdk.java.net/~shade/shenandoah/8u-workaround-jweak-2/webrev.01/
> 
> While we can intercept the bad closure during init-mark (and somehow disambiguate weak_oops closure
> for JNI weaks and other weak roots), it seems more straight-forward to intercept it near the  actual
> SRP use.
> 
> Testing: hotspot_tier3_gc_shenandoah (the regression test used to pass with the previous fix, failed
> with reverting the previous fix, and passed again after applying this fix variant)
> 
> Thanks,
> -Aleksey
>