RFR(M): 8248401: Refactor/unify RMI gc support functionality

[Thomas Schatzl]

Hi Stefan,

   thanks for your review.

On 03.08.20 13:30, Stefan Karlsson wrote:
> Hi Thomas,
> 
> Not a complete review, but regarding the ZGC change, I don't think it's 
> appropriate to add a callback to Universe/CollectedHeap to ZStatCycle. 
> Most functions in ZStat only collects and print statistics, and does not 
> trigger external events. I think moving it to the call would be cleaner:
> 
>    ~ZDriverGCScope() {
>     ...
>      // Update statistics
>      ZStatCycle::at_end(_gc_cause, boost_factor);
> 
>      // Update data used by soft reference policy
>      Universe::update_heap_info_at_gc();
> 
>      // Maybe add the call here?
>      ...
>    }
> 

Thank you for pointing out the appropriate place in ZGC. Done.

> Seeing this, it's also apparent that some of the "last_gc" info has 
> historically been recorded in Universe:
> 
> void Universe::update_heap_info_at_gc() {
>    _heap_capacity_at_last_gc = heap()->capacity();
>    _heap_used_at_last_gc     = heap()->used();
> }
> 
> while _last_whole_heap_examined_time_ns is recorded in CollectedHeap. I 
> think we should create a RFR to move the heap variables out of Universe.

Done, JDK-8250961.

In addition to above changes, I tried to move the new call closer to 
Universe::update_heap_info_at_gc() in a few places and improve naming of 
some local variables.

New webrevs:
http://cr.openjdk.java.net/~tschatzl/8248401/webrev.0_to_1 (diff)
http://cr.openjdk.java.net/~tschatzl/8248401/webrev.1 (full)

Reran the test 300 times with these changes.

Thanks,
   Thomas