[15] RFR 8242216: ObjectSampler::weak_oops_do() should not trigger barrier

[Erik Österlund]

Hi Zhengyu,

This change breaks ZGC. The raw oop may not have been relocated. It was 
not by accident that I used an access load instead of a raw load,
when I built the leak profiler support.
Since this kind of issue keeps on popping up, where you can't deal with 
access barriers because of some Shenandoah OOM handler,
perhaps your barriers need to be fixed instead to deal with these issues 
instead. I predict it is not the last time we have
to restructure the shared code because of Shenandoah's OOM handler.

Thanks,
/Erik

On 2020-04-06 20:22, Zhengyu Gu wrote:
> Hi,
>
> This is a similar problem as JDK-8237396.
>
> Shenandoah does not expect barriers on it GC paths. Otherwise, it 
> causes Shenandoah's OOM handler to fail.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8242216
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8242216/webrev.00/index.html
>
> Test:
>   tier1 (fastdebug and release) on Linux x86_64
>   Submit tests.
>
>
> Thanks,
>
> -Zhengyu
>