Make sure when we shrink an object that we store a filler first into the free memory before updatin…

src/objects.h

 // Copyright 2012 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 1793 matching lines @@
  public:
   // [map]: Contains a map which contains the object's reflective
   // information.
   inline Map* map();
   inline void set_map(Map* value);
   // The no-write-barrier version.  This is OK if the object is white and in
   // new space, or if the value is an immortal immutable object, like the maps
   // of primitive (non-JS) objects like strings, heap numbers etc.
   inline void set_map_no_write_barrier(Map* value);
 
+  // Get the map using acquire load.
+  inline Map* synchronized_map();
+  inline MapWord synchronized_map_word();
+
+  // Set the map using release store
+  inline void synchronized_set_map(Map* value);
+  inline void synchronized_set_map_word(MapWord map_word);
+
+  // Get the map using no barrier load.
+  inline Map* no_barrier_map();
+  inline MapWord no_barrier_map_word();
+
+  // Set the map using no barrier store.
+  inline void no_barrier_set_map(Map* value);
+  inline void no_barrier_set_map_word(MapWord map_word);
+
   // During garbage collection, the map word of a heap object does not
   // necessarily contain a map pointer.
   inline MapWord map_word();
   inline void set_map_word(MapWord map_word);
 
   // The Heap the object was allocated in. Used also to access Isolate.
   inline Heap* GetHeap();
 
   // Convenience method to get current isolate.
   inline Isolate* GetIsolate();
@@ skipping 1164 matching lines @@
 
 
 // Common superclass for FixedArrays that allow implementations to share
 // common accessors and some code paths.
 class FixedArrayBase: public HeapObject {
  public:
   // [length]: length of the array.
   inline int length();
   inline void set_length(int value);
 
+  // Get and set the length using acquire loads and release stores.
+  inline int synchronized_length();
+  inline void synchronized_set_length(int value);
+
   inline static FixedArrayBase* cast(Object* object);
 
   // Layout description.
   // Length is smi tagged when it is stored.
   static const int kLengthOffset = HeapObject::kHeaderSize;
   static const int kHeaderSize = kLengthOffset + kPointerSize;
 };
 
 
 class FixedDoubleArray;
@@ skipping 5742 matching lines @@
     Vector<const uint8_t> buffer_;
     State state_;
 
     friend class String;
   };
 
   // Get and set the length of the string.
   inline int length();
   inline void set_length(int value);
 
+  // Get and set the length of the string using acquire loads and release
+  // stores.
+  inline int synchronized_length();
+  inline void synchronized_set_length(int value);
+
   // Returns whether this string has only ASCII chars, i.e. all of them can
   // be ASCII encoded.  This might be the case even if the string is
   // two-byte.  Such strings may appear when the embedder prefers
   // two-byte external representations even for ASCII data.
   inline bool IsOneByteRepresentation();
   inline bool IsTwoByteRepresentation();
 
   // Cons and slices have an encoding flag that may not represent the actual
   // encoding of the underlying string.  This is taken into account here.
   // Requires: this->IsFlat()
@@ skipping 2016 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_