RFR: 8259839 SystemDictionary exports too much implementation [v2]

[Coleen Phillimore]

On Wed, 27 Jan 2021 06:10:28 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   return NULL for find_or_define_helper if pending exception
>
> Hi Coleen,
> 
> I can't quite convince myself that the changes in relation to potentially parallel definition are right, but that is mainly because I can't fully reconcile the existing comments in that area. A number of comments below.
> 
> Thanks,
> David

Re: @dholmes-ora your comment about parallel definition.  I'm trying to grok this myself, but apparently you can use AllowParallelClassDefine to enable parallel definition in custom class loader objects that are parallel capable.  I don't know why they have to be parallel capable but that's what the code does.  The placeholder entry for DEFINE_CLASS is used to synchronize parallel defines and implement this option.  There's a test for this that Volker wrote: in runtime/Metaspace/DefineClass.java.

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PR: https://git.openjdk.java.net/jdk/pull/2247