RFR: Make heap counters update completely asynchronous

[Aleksey Shipilev]

On 09/21/2017 06:44 PM, Roman Kennke wrote:
> Am 21.09.2017 um 18:40 schrieb Aleksey Shipilev:
>> http://cr.openjdk.java.net/~shade/shenandoah/concthread-periodic/webrev.01/
>>
>> This uses the periodic tasks facility provided by VM to update the counters asynchronously.
>> Allocation and GC paths are triggering the update, but do not perform the update themselves. This
>> allows to simplify allocation path, capture GCLAB allocations without risking deadlocks, etc.
>>
>> Testing: hotspot_gc_shenandoah, allocation benchmarks
>>
>> Thanks,
>> -Aleksey
>>
> I like it.
> 
> Do we really want/need to remove stuff from metaspaceCounters.cpp|hpp ?

These were our additions, along with TODO to clean that mess up.
Upstream does not have it.

-Aleksey