hg: jdk/sandbox: 8223951: Shenandoah: Only need to update thread roots during final update refs

[chris.hegarty at oracle.com]

Changeset: fe4c2de90b59
Author:    zgu
Date:      2019-05-17 11:47 -0400
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/fe4c2de90b59

8223951: Shenandoah: Only need to update thread roots during final update refs
Reviewed-by: shade

! src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.cpp
! src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.hpp
! src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp