RFR(S) 8235220: ClhsdbScanOops.java fails with sun.jvm.hotspot.types.WrongTypeException

[Chris Plummer]

Thanks!

On 4/13/20 12:48 PM, Alex Menkov wrote:
> Looks good.
>
> --alex
>
> On 04/13/2020 11:45, Chris Plummer wrote:
>> Ping! Can I get one more review please.
>>
>> thanks,
>>
>> Chris
>>
>> On 4/9/20 10:21 PM, Ioi Lam wrote:
>>> Hi Chris,
>>>
>>> Thanks for fixing this. It looks good to me.
>>>
>>> - Ioi
>>>
>>> On 4/9/20 9:44 PM, Chris Plummer wrote:
>>>> Hello,
>>>>
>>>> Please review the following:
>>>>
>>>> https://bugs.openjdk.java.net/browse/JDK-8235220
>>>> http://cr.openjdk.java.net/~cjplummer/8235220/webrev.00
>>>>
>>>> First off, thanks to Ioi for tracking this one down and proposing 
>>>> the fix.
>>>>
>>>> The test is executing the clhsdb "scanoops" command, which scans 
>>>> the specified heap address range looking for objects of the 
>>>> specified type (or all objects if no type is specified). The test 
>>>> determines the address range by first using clhsdb "universe" to 
>>>> get the start and end of the eden space. scanoops then iterates 
>>>> over this entire range, calling 
>>>> RobustOopDeterminator.oopLooksValid() on each oop as it iterates 
>>>> over the range. The problem is eventually you'll end up past the 
>>>> initialized part of the heap. That causes 
>>>> VirtualBaseConstructor.findDynamicTypeForAddress() to return null, 
>>>> resulting in throwing a WrongTypeException. 
>>>> RobustOopDeterminator.oopLooksValid() should catch this exception 
>>>> and return false when it happens.
>>>>
>>>> The CR mentions a few different failure modes. This only fixes the 
>>>> WrongTypeException failure. The NullPointerException is only on OSX 
>>>> and I believe is the same as JDK-8241158 [1], which happens when 
>>>> dumping the heap, so it seems probable that it is also turning up 
>>>> when scanning part of the heap. I think this bug was preventing us 
>>>> from ever seeing the WrongTypeException on OSX. Then there also 
>>>> JDK-8230731 [2] on Windows, which seems to prevent ever seeing the 
>>>> WrongTypeException on Windows.
>>>>
>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8241158
>>>> [2] https://bugs.openjdk.java.net/browse/JDK-8230731
>>>>
>>>> thanks,
>>>>
>>>> Chris
>>>
>>