Track JS allocations as they arrive with no affection on performance when tracking is switched off

src/heap-snapshot-generator.h

 // Copyright 2013 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 209 matching lines @@
 
 
 class HeapObjectsMap {
  public:
   explicit HeapObjectsMap(Heap* heap);
 
   Heap* heap() const { return heap_; }
 
   void SnapshotGenerationFinished();
   SnapshotObjectId FindEntry(Address addr);
-  SnapshotObjectId FindOrAddEntry(Address addr, unsigned int size);
-  void MoveObject(Address from, Address to);
+  SnapshotObjectId FindOrAddEntry(Address addr,
+                                  unsigned int size,
+                                  bool accessed = true);
+  void MoveObject(Address from, Address to, int size);
+  void NewObject(Address addr, int size);
+  void UpdateObjectSize(Address addr, int size);
   SnapshotObjectId last_assigned_id() const {
     return next_id_ - kObjectIdStep;
   }
 
   void StopHeapObjectsTracking();
   SnapshotObjectId PushHeapObjectsStats(OutputStream* stream);
   size_t GetUsedMemorySize() const;
 
   static SnapshotObjectId GenerateId(Heap* heap, v8::RetainedObjectInfo* info);
   static inline SnapshotObjectId GetNthGcSubrootId(int delta);
 
   static const int kObjectIdStep = 2;
   static const SnapshotObjectId kInternalRootObjectId;
   static const SnapshotObjectId kGcRootsObjectId;
   static const SnapshotObjectId kNativesRootObjectId;
   static const SnapshotObjectId kGcRootsFirstSubrootId;
   static const SnapshotObjectId kFirstAvailableObjectId;
 
+  int FindUntrackedObjects();
+
+  void UpdateHeapObjectsMap();
+
  private:
   struct EntryInfo {
   EntryInfo(SnapshotObjectId id, Address addr, unsigned int size)
       : id(id), addr(addr), size(size), accessed(true) { }
   EntryInfo(SnapshotObjectId id, Address addr, unsigned int size, bool accessed)
       : id(id), addr(addr), size(size), accessed(accessed) { }
     SnapshotObjectId id;
     Address addr;
     unsigned int size;
     bool accessed;
   };
   struct TimeInterval {
     explicit TimeInterval(SnapshotObjectId id) : id(id), size(0), count(0) { }
     SnapshotObjectId id;
     uint32_t size;
     uint32_t count;
   };
 
-  void UpdateHeapObjectsMap();
   void RemoveDeadEntries();
 
   SnapshotObjectId next_id_;
   HashMap entries_map_;
   List<EntryInfo> entries_;
   List<TimeInterval> time_intervals_;
   Heap* heap_;
 
   DISALLOW_COPY_AND_ASSIGN(HeapObjectsMap);
 };
@@ skipping 20 matching lines @@
 
   StringsStorage* names() { return &names_; }
 
   SnapshotObjectId FindObjectId(Address object_addr) {
     return ids_.FindEntry(object_addr);
   }
   SnapshotObjectId GetObjectId(Address object_addr, int object_size) {
     return ids_.FindOrAddEntry(object_addr, object_size);
   }
   Handle<HeapObject> FindHeapObjectById(SnapshotObjectId id);
-  void ObjectMoveEvent(Address from, Address to) { ids_.MoveObject(from, to); }
+  void ObjectMoveEvent(Address from, Address to, int size) {
+    ids_.MoveObject(from, to, size);
+  }
+  void NewObjectEvent(Address addr, int size) { ids_.NewObject(addr, size); }
+  void UpdateObjectSizeEvent(Address addr, int size) {
+    ids_.UpdateObjectSize(addr, size);
+  }
   SnapshotObjectId last_assigned_id() const {
     return ids_.last_assigned_id();
   }
   size_t GetUsedMemorySize() const;
 
+  int FindUntrackedObjects() { return ids_.FindUntrackedObjects(); }
+
+  void UpdateHeapObjectsMap() { ids_.UpdateHeapObjectsMap(); }
+
  private:
   bool is_tracking_objects_;  // Whether tracking object moves is needed.
   List<HeapSnapshot*> snapshots_;
   StringsStorage names_;
   // Mapping from HeapObject addresses to objects' uids.
   HeapObjectsMap ids_;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotsCollection);
 };
 
@@ skipping 347 matching lines @@
   friend class HeapSnapshotJSONSerializerIterator;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotJSONSerializer);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_SNAPSHOT_GENERATOR_H_