--- a/src/hotspot/share/gc/g1/g1ParScanThreadState.hpp	Wed Nov 20 14:16:29 2019 +0100
+++ b/src/hotspot/share/gc/g1/g1ParScanThreadState.hpp	Thu Nov 21 11:42:54 2019 +0100
@@ -74,7 +74,8 @@
   size_t* _surviving_young_words_base;
   // this points into the array, as we use the first few entries for padding
   size_t* _surviving_young_words;
-
+  // Number of elements in the array above.
+  size_t _surviving_words_length;
   // Indicates whether in the last generation (old) there is no more space
   // available for allocation.
   bool _old_gen_is_full;
@@ -152,7 +153,9 @@
   size_t lab_waste_words() const;
   size_t lab_undo_waste_words() const;
 
-  void flush(size_t* surviving_young_words);
+  // Pass locally gathered statistics to global state. Returns the total number of
+  // HeapWords copied.
+  size_t flush(size_t* surviving_young_words);
 
 private:
   #define G1_PARTIAL_ARRAY_MASK 0x2