Use NoBarrier_Load and NoBarrier_Store in FreeListCategory::Concatenate.

src/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1500 matching lines @@
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(FreeListNode);
 };
 
 
 // The free list category holds a pointer to the top element and a pointer to
 // the end element of the linked list of free memory blocks.
 class FreeListCategory {
  public:
   FreeListCategory() :
-      top_(NULL),
+      top_(0),
       end_(NULL),
       available_(0) {}
 
   intptr_t Concatenate(FreeListCategory* category);
 
   void Reset();
 
   void Free(FreeListNode* node, int size_in_bytes);
 
   FreeListNode* PickNodeFromList(int *node_size);
   FreeListNode* PickNodeFromList(int size_in_bytes, int *node_size);
 
   intptr_t EvictFreeListItemsInList(Page* p);
   bool ContainsPageFreeListItemsInList(Page* p);
 
   void RepairFreeList(Heap* heap);
 
-  FreeListNode** GetTopAddress() { return &top_; }
-  FreeListNode* top() const { return top_; }
-  void set_top(FreeListNode* top) { top_ = top; }
+  FreeListNode* top() const {
+    return reinterpret_cast<FreeListNode*>(NoBarrier_Load(&top_));
+  }
+
+  void set_top(FreeListNode* top) {
+    NoBarrier_Store(&top_, reinterpret_cast<AtomicWord>(top));
+  }
 
   FreeListNode** GetEndAddress() { return &end_; }
   FreeListNode* end() const { return end_; }
   void set_end(FreeListNode* end) { end_ = end; }
 
   int* GetAvailableAddress() { return &available_; }
   int available() const { return available_; }
   void set_available(int available) { available_ = available; }
 
   Mutex* mutex() { return &mutex_; }
 
   bool IsEmpty() {
-    return top_ == NULL;
+    return top() == 0;
   }
 
 #ifdef DEBUG
   intptr_t SumFreeList();
   int FreeListLength();
 #endif
 
  private:
-  FreeListNode* top_;
+  // top_ points to the top FreeListNode* in the free list category.
+  AtomicWord top_;
   FreeListNode* end_;
   Mutex mutex_;
 
   // Total available bytes in all blocks of this free list category.
   int available_;
 };
 
 
 // The free list for the old space.  The free list is organized in such a way
 // as to encourage objects allocated around the same time to be near each
@@ skipping 1383 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_