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

[Zhengyu Gu]

On 4/7/20 9:15 AM, Erik Österlund wrote:
> NVM, it seems like the closure takes care of that. Have you tried with 
> ZGC too, to sanity check that?

I ran the same tests that break Shenandoah with ZGC, they seem fine.

What else should I try?

Thanks,

-Zhengyu


> 
> /Erik
> 
> On 2020-04-07 15:09, Erik Österlund wrote:
>> 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
>>>
>>
>