Log histograms on shutdown when verbose logging is on

base/metrics/statistics_recorder.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
@@ skipping 149 matching lines @@
   static void ClearCallback(const std::string& histogram_name);
 
   // FindCallback retrieves the callback for the histogram referred to by
   // |histogram_name|, or a null callback if no callback exists for this
   // histogram. This method is thread safe.
   static OnSampleCallback FindCallback(const std::string& histogram_name);
 
   // Returns the number of known histograms.
   static size_t GetHistogramCount();
 
+  // Initializes logging histograms with --v=1. Safe to call several times.

[Lei Zhang, 2016/07/04 21:03:31]

s/several/multiple/

+  // Is called from ctor but for browser it seems that it is more useful to
+  // start logging after statistics recorder, so we need to init log-on-shutdown
+  // later.
+  static void InitLogOnShutdown();
+
   // Removes a histogram from the internal set of known ones. This can be
   // necessary during testing persistent histograms where the underlying
   // memory is being released.
   static void ForgetHistogramForTesting(base::StringPiece name);
 
   // Creates a local StatisticsRecorder object for testing purposes. All new
   // histograms will be registered in it until it is destructed or pushed
   // aside for the lifetime of yet another SR object. The destruction of the
   // returned object will re-activate the previous one. Always release SR
   // objects in the opposite order to which they're created.
   static std::unique_ptr<StatisticsRecorder> CreateTemporaryForTesting()
       WARN_UNUSED_RESULT;
 
   // Resets any global instance of the statistics-recorder that was created
   // by a call to Initialize().
   static void UninitializeForTesting();
 
  private:
   // We keep a map of callbacks to histograms, so that as histograms are
   // created, we can set the callback properly.
   typedef std::map<std::string, OnSampleCallback> CallbackMap;
 
   // We keep all |bucket_ranges_| in a map, from checksum to a list of
   // |bucket_ranges_|.  Checksum is calculated from the |ranges_| in
   // |bucket_ranges_|.
   typedef std::map<uint32_t, std::list<const BucketRanges*>*> RangesMap;
 
   friend struct DefaultLazyInstanceTraits<StatisticsRecorder>;
+  friend class StatisticsRecorderTest;
 
   // Imports histograms from global persistent memory. The global lock must
   // not be held during this call.
   static void ImportGlobalPersistentHistograms();
 
   // The constructor just initializes static members. Usually client code should
   // use Initialize to do this. But in test code, you can friend this class and
   // call the constructor to get a clean StatisticsRecorder.
   StatisticsRecorder();
 
+  // Initialize implementation but without lock. Caller should guard
+  // StatisticsRecorder by itlsef if needed (it isn't in unit tests).

[Lei Zhang, 2016/07/04 21:03:31]

type: "itself"

+  void InitLogOnShutdownWithoutLock();
+
   // These are copies of everything that existed when the (test) Statistics-
   // Recorder was created. The global ones have to be moved aside to create a
   // clean environment.
   std::unique_ptr<HistogramMap> existing_histograms_;
   std::unique_ptr<CallbackMap> existing_callbacks_;
   std::unique_ptr<RangesMap> existing_ranges_;
 
+  bool vlog_initialized_ = false;
+
   static void Reset();
   static void DumpHistogramsToVlog(void* instance);
 
   static HistogramMap* histograms_;
   static CallbackMap* callbacks_;
   static RangesMap* ranges_;
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_