8054818: Refactor HeapRegionSeq to manage heap region and auxiliary data

Let HeapRegionSeq manage the heap region and auxiliary data to decrease the amount of responsibilities of G1CollectedHeap, and encapsulate this work from other code.

Reviewed-by: jwilhelm, jmasa, mgerdin, brutisso

hotspot/src/share/vm/gc_implementation/g1/heapRegionSet.hpp

@@ -162,7 +162,7 @@ public:
 // diagnosing failures.
 class hrs_ext_msg : public hrs_err_msg {
 public:
-  hrs_ext_msg(HeapRegionSetBase* set, const char* message) : hrs_err_msg("%s","") {
+  hrs_ext_msg(HeapRegionSetBase* set, const char* message) : hrs_err_msg("%s", "") {
     set->fill_in_ext_msg(this, message);
   }
 };
@@ -192,13 +192,9 @@ public:
 };
 
 // A set that links all the regions added to it in a doubly-linked
-// list. We should try to avoid doing operations that iterate over
+// sorted list. We should try to avoid doing operations that iterate over
 // such lists in performance critical paths. Typically we should
-// add / remove one region at a time or concatenate two lists. There are
-// two ways to treat your lists, ordered and un-ordered. All un-ordered
-// operations are done in constant time. To keep a list ordered only use
-// add_ordered() to add elements to the list. If a list is not ordered
-// from start, there is no way to sort it later.
+// add / remove one region at a time or concatenate two lists.
 
 class FreeRegionListIterator;
 
@@ -210,13 +206,13 @@ private:
   HeapRegion* _tail;
 
   // _last is used to keep track of where we added an element the last
-  // time in ordered lists. It helps to improve performance when adding
-  // several ordered items in a row.
+  // time. It helps to improve performance when adding several ordered items in a row.
   HeapRegion* _last;
 
   static uint _unrealistically_long_length;
 
-  void add_as_head_or_tail(FreeRegionList* from_list, bool as_head);
+  inline HeapRegion* remove_from_head_impl();
+  inline HeapRegion* remove_from_tail_impl();
 
 protected:
   virtual void fill_in_ext_msg_extra(hrs_ext_msg* msg);
@@ -232,8 +228,11 @@ public:
 
   void verify_list();
 
-  HeapRegion* head() { return _head; }
-  HeapRegion* tail() { return _tail; }
+#ifdef ASSERT
+  bool contains(HeapRegion* hr) const {
+    return hr->containing_set() == this;
+  }
+#endif
 
   static void set_unrealistically_long_length(uint len);
 
@@ -242,55 +241,20 @@ public:
   // is determined by hrs_index.
   inline void add_ordered(HeapRegion* hr);
 
-  // It adds hr to the list as the new head. The region should not be
-  // a member of another set.
-  inline void add_as_head(HeapRegion* hr);
-
-  // It adds hr to the list as the new tail. The region should not be
-  // a member of another set.
-  inline void add_as_tail(HeapRegion* hr);
-
-  // It removes and returns the head of the list. It assumes that the
-  // list is not empty so it will return a non-NULL value.
-  inline HeapRegion* remove_head();
-
-  // Convenience method.
-  inline HeapRegion* remove_head_or_null();
-
-  // Removes and returns the last element (_tail) of the list. It assumes
-  // that the list isn't empty so that it can return a non-NULL value.
-  inline HeapRegion* remove_tail();
-
-  // Convenience method
-  inline HeapRegion* remove_tail_or_null();
-
   // Removes from head or tail based on the given argument.
-  inline HeapRegion* remove_region(bool from_head);
+  HeapRegion* remove_region(bool from_head);
 
   // Merge two ordered lists. The result is also ordered. The order is
   // determined by hrs_index.
   void add_ordered(FreeRegionList* from_list);
 
-  // It moves the regions from from_list to this list and empties
-  // from_list. The new regions will appear in the same order as they
-  // were in from_list and be linked in the beginning of this list.
-  void add_as_head(FreeRegionList* from_list);
-
-  // It moves the regions from from_list to this list and empties
-  // from_list. The new regions will appear in the same order as they
-  // were in from_list and be linked in the end of this list.
-  void add_as_tail(FreeRegionList* from_list);
-
   // It empties the list by removing all regions from it.
   void remove_all();
 
-  // It removes all regions in the list that are pending for removal
-  // (i.e., they have been tagged with "pending_removal"). The list
-  // must not be empty, target_count should reflect the exact number
-  // of regions that are pending for removal in the list, and
-  // target_count should be > 1 (currently, we never need to remove a
-  // single region using this).
-  void remove_all_pending(uint target_count);
+  // Remove all (contiguous) regions from first to first + num_regions -1 from
+  // this list.
+  // Num_regions must be > 1.
+  void remove_starting_at(HeapRegion* first, uint num_regions);
 
   virtual void verify();
 
@@ -298,7 +262,7 @@ public:
 };
 
 // Iterator class that provides a convenient way to iterate over the
-// regions of a HeapRegionLinkedList instance.
+// regions of a FreeRegionList.
 
 class FreeRegionListIterator : public StackObj {
 private:
@@ -324,7 +288,7 @@ public:
   }
 
   FreeRegionListIterator(FreeRegionList* list) : _curr(NULL), _list(list) {
-    _curr = list->head();
+    _curr = list->_head;
   }
 };