RFR: 8220240: Refactor shared dirty card queue

[Thomas Schatzl]

Hi,

On Fri, 2019-03-08 at 19:20 -0500, Kim Barrett wrote:
> Please review this change which adds a new class,
> G1SharedDirtyCardQueue, in order to allow some simplifications of the
> PtrQueue class and classes derived from it.
> 
[...]
> G1SharedDirtyCardQueue is still lock-based, using
> Shared_DirtyCardQ_lock, which still needs to have access-related
> rank. It could be made lock-free, if the elimination of that access-
> related lock seems sufficiently important to warrant the extra
> complexity. The situation where the shared queue is needed is
> extremely rare, so contention for the lock isn't an issue.  This
> can be addressed in a followup improvement.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8220240
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8220240/open.00/
> 
> I'll update copyrights before pushing.

Some very minor issues:

- g1DirtyCardQueue.hpp:70:71: superfluous linebreaks

- please add a sentence/comment what G1SharedDirtyCardQueue is at the
declaration.

Looks good otherwise. Do not need to re-review these changes.

Thanks,
  Thomas