Adding api to get last gc object statistics for chrome://tracing.

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 4795 matching lines @@
   const char* space_name_;
   size_t space_size_;
   size_t space_used_size_;
   size_t space_available_size_;
   size_t physical_space_size_;
 
   friend class Isolate;
 };
 
 
+class V8_EXPORT HeapObjectStatistics {
+ public:
+  HeapObjectStatistics();
+  const char* object_type() { return object_type_; }
+  size_t object_count() { return object_count_; }
+  size_t object_size() { return object_size_; }

[ulan, 2015/05/06 12:46:02]

You probably also want a notion of sub-type or secondary type.  For example a
single code object can have multiple HeapObjectStatistics:
- one with type "CODE_TYPE",
- one with type "CODE_TYPE_<code-kind>",
- one with type "CODE_TYPE_<code-age".

So HeapObjectStatistics can share objects. Sum of object_size() will not be the
correct total as it double counts some objects.

[ssid, 2015/05/07 13:53:03]

As discussed offline, the sub-types are just given by the way the object is
named, so this object remains the same.

+
+ private:
+  const char* object_type_;
+  size_t object_count_;
+  size_t object_size_;
+
+  friend class Isolate;
+};
+
+
 class RetainedObjectInfo;
 
 
 /**
  * FunctionEntryHook is the type of the profile entry hook called at entry to
  * any generated function when function-level profiling is enabled.
  *
  * \param function the address of the function that's being entered.
  * \param return_addr_location points to a location on stack where the machine
  *    return address resides. This can be used to identify the caller of
@@ skipping 368 matching lines @@
    * \param space_statistics The HeapSpaceStatistics object to fill in
    *   statistics.
    * \param index The index of the space to get statistics from, which ranges
    *   from 0 to NumberOfHeapSpaces() - 1.
    * \returns true on success.
    */
   bool GetHeapSpaceStatistics(HeapSpaceStatistics* space_statistics,
                               size_t index);
 
   /**
+   * Returns the number of types of objects in the heap.
+   */
+  size_t NumberOfHeapObjectsTypes();

[ulan, 2015/05/06 12:46:02]

Strictly speaking this is not the number of heap object types. This is the
number of heap object statistics that we track (which is more than the actual
heap object types). Can we make it more explicit in the name that this is about
statistics and not generic heap object types?

[ssid, 2015/05/07 13:53:03]

Done.

+
+  /**
+   * Get statistics about objects in the heap.
+   *
+   * \param object_statistics The HeapObjectStatistics object to fill in
+   *   statistics of objects of given type, which were live in the previous GC.
+   * \param type_index The index of the type of object to fill details about,
+   *   which ranges from 0 to NumberOfHeapObjectsTypes() - 1.
+   * \returns true on success.
+   */
+  bool GetLastGcObjectStatistics(HeapObjectStatistics* object_statistics,

[ulan, 2015/05/06 12:46:02]

GetHeapObjectStatisticsAtLastGC(...) to be consistent with other
GetHeap*Statistics functions.

[ssid, 2015/05/07 13:53:03]

Done.

+                                 size_t type_index);
+
+  /**
    * Get a call stack sample from the isolate.
    * \param state Execution state.
    * \param frames Caller allocated buffer to store stack frames.
    * \param frames_limit Maximum number of frames to capture. The buffer must
    *                     be large enough to hold the number of frames.
    * \param sample_info The sample info is filled up by the function
    *                    provides number of actual captured stack frames and
    *                    the current VM state.
    * \note GetStackSample should only be called when the JS thread is paused or
    *       interrupted. Otherwise the behavior is undefined.
@@ skipping 2805 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // V8_H_