RFR(S): 8173743: Failures during class definition can lead to memory leaks in metaspace

[David Holmes]

On 7/02/2017 10:18 AM, Coleen Phillimore wrote:
>
> Volker,  This looks really good.  Thank you for fixing this!  I can't
> see any risk to jdk9 so I think this seems fine to check in now, even
> though it's been a bug since jdk8.
>
> I guess you can check this in yourself with the demo-submit tool?
> Otherwise, I will sponsor it.

It still needs to be sponsored. The demo-submit is still a work in 
progress and does not cover everything an internal JPRT submission would,

Thanks,
David
-----

> Thanks,
> Coleen
>
>
> On 2/6/17 1:40 PM, Volker Simonis wrote:
>> Hi,
>>
>> can somebody please review the following change:
>>
>> http://cr.openjdk.java.net/~simonis/webrevs/2017/8173743.v1/
>> https://bugs.openjdk.java.net/browse/JDK-8173743
>>
>> It fixes some problems during class definitions where instance klasses
>> can leak into the metaspace in cases where the class definition fails
>> after the class was successfully loaded from the bytecode stream.
>>
>> There are actually two cases to consider:
>>
>> 1. If we load the same class several times into the same class loader,
>> we will get LinkageErrors after the first successful load. But
>> nevertheless we will first construct a new instanceKlass for each new
>> load attempt and this instanceKlass will never be deleted.
>>
>> 2. If we have a parallel capable class loader, set
>> -XX:-UnsyncloadClass and/or -XX:+AllowParallelDefineClass and load a
>> class from several threads at the same time in parallel, it can happen
>> that we create several instance klasses for the same class. At the end
>> only one of them will be added to the system dictionary, but all the
>> other ones will never be deleted. Notice that if we run this scenario
>> without setting either of -XX:-UnsyncloadClass or
>> -XX:+AllowParallelDefineClass, this scenario will degrade into the
>> case above and we will get LinkageErrors for all but the first
>> successful load.
>>
>> The change comes with a regression test which checks for the two cases
>> just describe and also for the failing class redefinition case, which
>> currently doesn't produce a memory leak.
>>
>> I've already committed this to the hs-demo-submit/hotspot/ forest and
>> it went through without a problem. So in theory it should have passed
>> the internal JPRT tests although I'm not sure if the test set of the
>> "demo-submit" forest and the real hotspot repo are exactly the same
>> (CC'ed Tim and Brian).
>>
>> Thank you and best regards,
>> Volker
>