--- old/src/hotspot/share/gc/z/zMark.cpp	2019-08-05 15:48:10.356731137 +0200
+++ new/src/hotspot/share/gc/z/zMark.cpp	2019-08-05 15:48:10.111723139 +0200
@@ -634,17 +634,16 @@
 class ZMarkConcurrentRootsTask : public ZTask {
 private:
   SuspendibleThreadSetJoiner          _sts_joiner;
-  ZConcurrentRootsIterator            _roots;
+  ZConcurrentRootsIteratorClaimStrong _roots;
   ZMarkConcurrentRootsIteratorClosure _cl;
 
 public:
   ZMarkConcurrentRootsTask(ZMark* mark) :
       ZTask("ZMarkConcurrentRootsTask"),
-      _sts_joiner(true /* active */),
-      _roots(ClassLoaderData::_claim_strong),
+      _sts_joiner(),
+      _roots(),
       _cl() {
     ClassLoaderDataGraph_lock->lock();
-    ClassLoaderDataGraph::clear_claimed_marks();
   }
 
   ~ZMarkConcurrentRootsTask() {