RFR: 8209345: Merge SATBMarkQueueFilter into SATBMarkQueueSet

[Kim Barrett]

> On Aug 13, 2018, at 6:09 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi,
> 
> On Sun, 2018-08-12 at 22:08 -0400, Kim Barrett wrote:
>> Please review this change that eliminates SATBMarkQueueFilter in
>> favor
>> of an extension to SATBMarkQueueSet.  […]
>> 
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8209345/open.00/
>> 
>> Testing:
>> Mach5 tier1-3, hs-tier4-5, in conjunction with JDK-8209346 and JDK-
>> 8209347.
>> Locally tier1 and hotspot_gc without those other changes.
>> 
> 
>  - I think the SATBMarkQueueSet's destructor should be virtual, given
> that there will be a second implementor with unknown functionality (and
> in general I prefer to have virtual destructors as soon there is any
> virtual method). Also the SATBBufferClosure's one.

These destructors (and similarly for PtrQueue and PtrQueueSet) are
protected, which is the other approach [1] to ensuring there will be
no destructor slicing. Objects in these hierarchies are never
destroyed via a base class pointer, so don't need a public base class
destructor (which should indeed be virtual).

[1] "50. Make base class destructors public and virtual or protected
and nonvirtual", C++ Coding Standards, Sutter & Alexandrescu.

> Looks good otherwise.
> 
> Thanks,
>  Thomas

Thanks.