RFR: Avoid Full STW GC on System.gc()

[Roman Kennke]

Am 05.09.2017 um 21:04 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/concthread-explicitgc/webrev.01/
> 
> Does what is says: triggers concurrent cycle on System.gc() now. Tests DisableExplicitGC and
> ExplicitGCInvokesConcurrent options too.
> 
> Testing: hotspot_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 

Ok. Except the comment might be a bit confusing:

+
+  // In current Shenandoah, default System.gc() means full
stop-the-world GC, which might
+  // surprise users. Replace it with full concurrent GC, unless user
really wants otherwise.

When I read this after the patch has been pushed, 'current Shenandoah'
has a different meaning than now :-)

Otherwise good.