RFR (S) 8247845: Shenandoah: refactor TLAB/GCLAB retirement code

[Roman Kennke]

I forgot to review it, sorry for the late reply.

The patch looks good to me.

Thank you,
Roman

On Thu, 2020-06-18 at 18:30 +0200, Aleksey Shipilev wrote:
> RFE:
>   https://bugs.openjdk.java.net/browse/JDK-8247845
> 
> Fix;
>   http://cr.openjdk.java.net/~shade/8247845/webrev.01/
> 
> Current TLAB/GCLAB retirement code is all over the place. Sometimes
> we retire GCLABs twice.
> Sometimes we resize TLABs twice. This hopefully makes the things more
> clear by lifting things out of
> CollectedHeap::ensure_parsability and specializing it for Shenandoah
> use cases.
> 
> Testing: hotspot_gc_shenandoah {fastdebug,release}; tier{1,2} with
> Shenandoah; benchmarks (running)
>