RFR: 8179387: Factor out CMS specific code from GenCollectedHeap into its own subclass

[Roman Kennke]

Am 03.07.2017 um 11:13 schrieb Roman Kennke:
> Am 03.07.2017 um 09:35 schrieb Mikael Gerdin:
>> Hi Roman,
>>
>> On 2017-06-30 18:32, Roman Kennke wrote:
>>> I came across one problem using this approach: We will have 2 instances
>>> of CollectedHeap around, where there's usually only 1, and some code
>>> expects only 1. For example, in CollectedHeap constructor, we create new
>>> PerfData variables, and we now create them 2x, which leads to an assert
>>> being thrown. I suspect there is more code like that.
>>>
>>> I will attempt to refactor this a little more, maybe it's not that bad,
>>> but it's probably not worth spending too much time on it.
>> I think refactoring the code to not expect a singleton CollectedHeap
>> instance is a bit too much.
>> Perhaps there is another way to share common code between Serial and
>> CMS but that might require a bit more thought.
> Yeah, definitely. I hit another difficulty: pretty much the same issues
> that I'm having with GenCollectedHeap/CMSHeap/CollectedHeap now show up
> with Generation and its subclasses..
>
> How about we push the original patch that I've posted, and work from
> there? In fact, I *have* found some little things I would change (some
> more if (UseConcMarkSweepGC) branches in GenCollectedHeap that I have
> overlooked in my first pass...)

So here's the little change (two more places in genCollectedHeap.hpp
where UseConcMarkSweepGC was used to alter behaviour:

http://cr.openjdk.java.net/~rkennke/8179387/webrev.02/
<http://cr.openjdk.java.net/%7Erkennke/8179387/webrev.02/>

Ok to push this?

Roman