diff a/src/hotspot/share/gc/z/zWeakRootsProcessor.cpp b/src/hotspot/share/gc/z/zWeakRootsProcessor.cpp
--- a/src/hotspot/share/gc/z/zWeakRootsProcessor.cpp
+++ b/src/hotspot/share/gc/z/zWeakRootsProcessor.cpp
@@ -60,10 +60,14 @@
 public:
   ZProcessConcurrentWeakRootsTask() :
       ZTask("ZProcessConccurentWeakRootsTask"),
       _concurrent_weak_roots() {}
 
+  ~ZProcessConcurrentWeakRootsTask() {
+    _concurrent_weak_roots.notify();
+  }
+
   virtual void work() {
     ZPhantomCleanOopClosure cl;
     _concurrent_weak_roots.oops_do(&cl);
   }
 };