hg: jdk/sandbox: 8241081: Shenandoah: Do not modify update-watermark concurrently

[chris.hegarty at oracle.com]

Changeset: 56e78301b358
Author:    rkennke
Date:      2020-03-17 11:49 +0100
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/56e78301b358

8241081: Shenandoah: Do not modify update-watermark concurrently
Reviewed-by: shade

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