--- old/src/share/vm/gc/shared/gcId.hpp	2015-09-09 16:12:52.563861802 +0200
+++ new/src/share/vm/gc/shared/gcId.hpp	2015-09-09 16:12:52.447861806 +0200
@@ -30,22 +30,20 @@
 class GCId : public AllStatic {
   friend class GCIdMark;
   static uint _next_id;
+  static uint _current_id;
   static const uint UNDEFINED = (uint)-1;
   static const uint create();
+  static void set_current(uint gc_id) { _current_id = gc_id; }
 
  public:
-  // Returns the currently active GC id. Asserts that there is an active GC id.
   static const uint current();
-  // Same as current() but can return undefined() if no GC id is currently active
-  static const uint current_raw();
-  static const uint undefined() { return UNDEFINED; }
 };
 
 class GCIdMark {
-  uint _gc_id;
+  uint _previous_gc_id;
+  DEBUG_ONLY(uint _gc_id;)
  public:
   GCIdMark();
-  GCIdMark(uint gc_id);
   ~GCIdMark();
 };