RFR 8231293: Shenandoah: Traversal fails JVMTI tests

[Zhengyu Gu]

On 9/23/19 10:00 AM, Roman Kennke wrote:
> Why is that a problem?
> 
> As far as I know, we don't concurrently clean native roots with 
> traversal GC. Or do we?

No. But when walking jvmti weak roots (in fixup roots or parallel 
cleaning), it triggers load barrier.

-Zhengyu

> 
> Roman
> 
>> The problem is caused by LRB trying to evacuate dead oops.
>> At this point, traversal is completed, therefore, no more evacuation 
>> should happen. We should complete the marking bitmap and arm native 
>> barrier to prevent from-space oops from leaking to system.
>>
>> There are duplicated works among fixup roots and parallel cleaning, 
>> let's address them in DKJDK-8231324.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8231293
>> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8231293/webrev.00/index.html
>>
>> Test:
>>    hotspot_gc_shenandoah (fastdebug and release)
>>    vmTestbase/nsk/jvmti (fastdebug and release) normal and traversal
>>    modes.
>>
>> Thanks,
>>
>> -Zhengyu
>>