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

[Aleksey Shipilev]

Thanks!

Roman, does this look sane to you?

-Aleksey

On 08/15/2018 04:59 PM, Zhengyu Gu wrote:
> 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
>>