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 77 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 all registered histograms in a map, indexed by the hash of the
+  // name of the histogram.
+  typedef std::map<uint64_t, 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;
 
@@ skipping 21 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_