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List:       openjdk-hotspot-gc-dev
Subject:    Re: RFR: 8038925: Java 7 with G1 crashes in dump_instance_fields using jmap or jcmd without fullgc
From:       Andreas Eriksson <andreas.eriksson () oracle ! com>
Date:       2014-04-30 12:14:25
Message-ID: 5360E921.5040507 () oracle ! com
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Thomas showed that this reproduces on jdk9 as well, so I'm re-targeting 
(and maybe reworking) the fix.
Right now it looks like changes related to permgen removal makes it only 
reproduce on debug builds for jdk9 though.
More info can be found in the jira bug.

Regards,
Andreas

On 2014-04-25 15:57, Andreas Eriksson wrote:
> I saw no obvious reason why it doesn't reproduce on jdk8 or jdk9.
> Maybe someone with better knowledge of G1 can say.
> Could it have something to do with the metaspace rewrites?
>
> /Andreas
>
> On 2014-04-25 15:21, Andreas Eriksson wrote:
>> In addition, this particular test doesn't reproduce on jdk8 or jdk9 
>> for some reason.
>> I will take a quick look and see if I can spot why.
>>
>> /Andreas
>>
>> On 2014-04-25 15:14, Mikael Gerdin wrote:
>>> On Friday 25 April 2014 14.53.29 Thomas Schatzl wrote:
>>>> Hi,
>>>>
>>>> On Fri, 2014-04-25 at 14:17 +0200, Andreas Eriksson wrote:
>>>>> Hi,
>>>>>
>>>>> Could I have a review for this G1 jdk7 only fix please?
>>>>    why is this change only necessary for jdk7?
>>> The idea was that for 9 and 8u40+ we will need a separate way to 
>>> handle this
>>> anyway due to class unloading (as previously discussed).
>>>
>>> We may or may not want to get this fix into 8u20, I'd like to hear 
>>> your input
>>> on that Thomas.
>>>
>>> /Mikael
>>>
>>>>> Description:
>>>>> When using G1 and doing a heap dump while no fullgc has been done,
>>>>> hotspot crashes.
>>>>> This is because G1CollectedHeap::safe_object_iterate uses
>>>>> ContiguousSpace::object_iterate_from, which does not avoid dead 
>>>>> objects
>>>>> that can still be on the heap when using G1.
>>>>>
>>>>> The fix adds a G1 specific safe_object_iterate code path that avoids
>>>>> dead objects.
>>>>>
>>>>> http://cr.openjdk.java.net/~aeriksso/8038925/webrev.00/
>>>>> https://bugs.openjdk.java.net/browse/JDK-8038925
>>>>>
>>>>> Thanks to Mikael Gerdin for his help with this.
>>>> Thanks,
>>>> Thomas
>>
>

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