RFR: 8175318: Performance issue regarding local JNI references

[Kim Barrett]

> On Jul 19, 2017, at 4:11 AM, Aleksey Shipilev <shade at redhat.com> wrote:
> 
> Hi Kim,
> 
> On 07/19/2017 01:39 AM, Kim Barrett wrote:
>> Webrev:
>> http://cr.openjdk.java.net/~kbarrett/8175318/hotspot.00/
> 
> This makes sense to me.
> 
> Do you want to introduce a utility method that clearly captures "top == 0", and
> pair it with "clear()"? E.g.:
> 
>  void clear() { _top == 0: } // already have one
>  bool is_clear() { return _top == 0; }
> 
> Thanks,
> -Aleksey

Thanks for reviewing.

I decided not to bother with is_clear() right now.  There would just be the couple of
uses in the vicinity of this change, plus a !is_clear() in print_statistics.  If anything,
I’d be inclined to remove the unused clear() function. I looked at the places where
we zero _top, and I don’t think any of them are particularly improved by calling clear().