src/hotspot/share/oops/klass.hpp

   // java/lang/Class instance mirroring this class
   OopHandle _java_mirror;
   // Superclass
   Klass*      _super;
   // First subclass (NULL if none); _subklass->next_sibling() is next one
-  Klass*      _subklass;
+  Klass* volatile _subklass;
   // Sibling link (or NULL); links all subklasses of a klass
-  Klass*      _next_sibling;
+  Klass* volatile _next_sibling;
 
   // All klasses loaded by a class loader are chained through these links
   Klass*      _next_link;
 
   // The VM's representation of the ClassLoader used to load this class.

@@ -282,12 +282,13
 
   // Note: for instances layout_helper() may include padding.
   // Use InstanceKlass::contains_field_offset to classify field offsets.
 
   // sub/superklass links
-  Klass* subklass() const              { return _subklass; }
-  Klass* next_sibling() const          { return _next_sibling; }
+  Klass* subklass(bool log = false) const;
+  Klass* next_sibling(bool log = false) const;
+
   InstanceKlass* superklass() const;
   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
 
   void set_next_link(Klass* k) { _next_link = k; }
   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.

@@ -666,10 +667,12
   // Load the klass's holder as a phantom. This is useful when a weak Klass
   // pointer has been "peeked" and then must be kept alive before it may
   // be used safely.
   oop holder_phantom() const;
 
+  void clean_subklass();
+
   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
   static void clean_subklass_tree() {
     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
   }