RFR 8204947: Port ShenandoahTaskTerminator to mainline and make it default

[zgu at redhat.com]

Hi Thomas,


> However, when trying this out I rarely get an assertion failure in
> taskqueue.cpp:234.
> 
Ha, this indeed my bug, could you try following patch? or I can
generate new webrev.

diff -r 26bd32dafb9b src/hotspot/share/gc/shared/owstTaskTerminator.cpp
--- a/src/hotspot/share/gc/shared/owstTaskTerminator.cpp        Wed Dec
05 10:12:32 2018 -0500
+++ b/src/hotspot/share/gc/shared/owstTaskTerminator.cpp        Wed Dec
05 13:40:00 2018 -0500
@@ -37,6 +37,7 @@
 
   // Single worker, done
   if (_n_threads == 1) {
+    _offered_termination = 1;
     return true;
   }

Thanks,

-Zhengyu

> From what I understand, the effect of both variants should be the
> same,
> so I would like to investigate this further. So far it looks like a
> (pre-existing, benign?) G1 bug.
> 
> Thanks,
>   Thomas
> 
>