New heap profiler: implement fast retaining sizes approximation.

include/v8-profiler.h

 // Copyright 2010 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.
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@@ skipping 264 matching lines @@
 
   /**
    * Returns the number of instances. Only applicable to aggregated
    * heap snapshots.
    */
   int GetInstancesCount() const;
 
   /** Returns node's own size, in bytes. */
   int GetSelfSize() const;
 
-  /** Returns node's network (self + reachable nodes) size, in bytes. */
-  int GetReachableSize() const;
-
   /**
    * Returns node's retained size, in bytes. That is, self + sizes of
    * the objects that are reachable only from this object. In other
    * words, the size of memory that will be reclaimed having this node
    * collected.
+   *
+   * Exact retained size calculation has O(N) (number of nodes)
+   * computational complexity, while approximate has O(1). It is
+   * assumed that initially heap profiling tools provide approximate
+   * sizes for all nodes, and then exact sizes are calculated for the
+   * most 'interesting' nodes.
    */
-  int GetRetainedSize() const;
+  int GetRetainedSize(bool exact) const;
 
   /** Returns child nodes count of the node. */
   int GetChildrenCount() const;
 
   /** Retrieves a child by index. */
   const HeapGraphEdge* GetChild(int index) const;
 
   /** Returns retainer nodes count of the node. */
   int GetRetainersCount() const;
 
   /** Returns a retainer by index. */
   const HeapGraphEdge* GetRetainer(int index) const;
 
   /** Returns the number of simple retaining paths from the root to the node. */
   int GetRetainingPathsCount() const;
 
   /** Returns a retaining path by index. */
   const HeapGraphPath* GetRetainingPath(int index) const;
+
+  /**
+   * Returns a dominator node. This is the node that participates in every

[Søren Thygesen Gjesse, 2010/11/22 09:49:48]

is the -> is a?

[mnaganov (inactive), 2010/11/22 16:43:56]

Done.

+   * path from the snapshot root to the current node.
+   */
+  const HeapGraphNode* GetDominatorNode() const;
 };
 
 
 class V8EXPORT HeapSnapshotsDiff {
  public:
   /** Returns the root node for added nodes. */
   const HeapGraphNode* GetAdditionsRoot() const;
 
   /** Returns the root node for deleted nodes. */
   const HeapGraphNode* GetDeletionsRoot() const;
@@ skipping 82 matching lines @@
 };
 
 
 }  // namespace v8
 
 
 #undef V8EXPORT
 
 
 #endif  // V8_V8_PROFILER_H_