src/hotspot/share/oops/klass.cpp

Concurrent class unloading

 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
   if (!ClassUnloading || !unloading_occurred) {
     return;
   }
 
+  MutexLockerEx ml(UseZGC ? Compile_lock : NULL);
   Klass* root = SystemDictionary::Object_klass();
   Stack<Klass*, mtGC> stack;
 
   stack.push(root);
   while (!stack.is_empty()) {