Reorganize histograms for persistence.

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 10 matching lines @@
 #include "base/gtest_prod_util.h"
 #include "base/lazy_instance.h"
 #include "base/metrics/histogram_base.h"
 
 namespace base {
 
 class BucketRanges;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
+  // We keep all registered histograms in a map, from name to histogram.
+  typedef std::map<uint64_t, HistogramBase*> HistogramMap;

[Alexei Svitkine (slow), 2015/12/04 18:21:00]

This should be in the private: section below. Also, update the comment please.

[bcwhite, 2015/12/04 19:34:47]

Done.  It actually has to be up top so as to be previously defined when it is
used by something in the "public" section... but that "something" got moved into
the other CL so this will have to migrate over there.

+
  public:
   typedef std::vector<HistogramBase*> Histograms;
 
   // Initializes the StatisticsRecorder system. Safe to call multiple times.
   static void Initialize();
 
   // Find out if histograms can now be registered into our list.
   static bool IsActive();
 
   // Register, or add a new histogram to the collection of statistics. If an
@@ skipping 47 matching lines @@
   // ClearCallback clears any callback set on the histogram referred to by
   // |histogram_name|. This method is thread safe.
   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);
 
  private:
-  // HistogramNameRef holds a weak const ref to the name field of the associated
-  // Histogram object, allowing re-use of the underlying string storage for the
-  // map keys. The wrapper is required as using "const std::string&" as the key
-  // results in compile errors.
-  struct HistogramNameRef {
-    explicit HistogramNameRef(const std::string& name) : name_(name) {};
-
-    // Operator < is necessary to use this type as a std::map key.
-    bool operator<(const HistogramNameRef& other) const {
-      return name_ < other.name_;
-    }
-
-    // Weak, owned by the associated Histogram object.
-    const std::string& name_;
-  };
-
-  // We keep all registered histograms in a map, from name to histogram.
-  typedef std::map<HistogramNameRef, HistogramBase*> HistogramMap;
-
   // 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, std::list<const BucketRanges*>*> RangesMap;
 
   friend struct DefaultLazyInstanceTraits<StatisticsRecorder>;
@@ skipping 20 matching lines @@
 
   // Lock protects access to above maps.
   static base::Lock* lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_