RFR: 8178836: Improve PtrQueue index abstraction

[Kim Barrett]

Still looking for a second review.

> On Apr 22, 2017, at 1:19 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
>> On Apr 21, 2017, at 7:00 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
>>> Minor nits:
>>> 
>>> *) On first scan, "limit" reads as the loop variable, because it is the only
>>> initialization in init block. Move it out?
>>> 
>>> 161   for (size_t limit = buffer_size(); i < limit; ++i) {
>> 
>> OK.
> 
> Updated webrev:
> full: http://cr.openjdk.java.net/~kbarrett/8178836/hotspot.01/
> incr: http://cr.openjdk.java.net/~kbarrett/8178836/hotspot.01.inc/