RFR: Make heap counters update completely asynchronous

[Aleksey Shipilev]

On 09/21/2017 06:40 PM, Aleksey Shipilev wrote:
> 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.

Actually, let it be more resilient for the case WatcherThread crashes: there is some protection
against that, but I think the failure would not be reliably reported. Capture that case in
ShenandoahConcurrentThread itself after GC cycle.

http://cr.openjdk.java.net/~shade/shenandoah/concthread-periodic/webrev.02/

-Aleksey