--- old/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	2015-03-31 14:52:48.907189455 +0200
+++ new/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	2015-03-31 14:52:48.791189460 +0200
@@ -1106,6 +1106,17 @@
   // region has no marks. Return true if all is well, false if errors
   // are detected.
   bool verify_bitmaps(const char* caller, HeapRegion* hr);
+
+  // True if the heap_lock is held by the a non-gc thread invoking a gc
+  // operation.
+  bool _thread_holds_heap_lock_for_gc;
+  // Returns true if the calling thread holds the heap lock,
+  // or the calling thread is a par gc thread and the heap_lock is held
+  // by the vm thread doing a gc operation.
+  bool heap_lock_held_for_gc();
+
+  void set_heap_lock_held_for_gc(bool value) { _thread_holds_heap_lock_for_gc = value; }
+
 #endif // PRODUCT
 
   // If G1VerifyBitmaps is set, verify that the marking bitmaps for