base/metrics/histogram_samples.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_METRICS_HISTOGRAM_SAMPLES_H_
   6 #define BASE_METRICS_HISTOGRAM_SAMPLES_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/metrics/histogram_base.h"
  10 #include "base/memory/scoped_ptr.h"
  11
  12 class Pickle;
  13 class PickleIterator;
  14
  15 namespace base {
  16
  17 class SampleCountIterator;
  18
  19 // HistogramSamples is a container storing all samples of a histogram.
  20 class BASE_EXPORT HistogramSamples {
  21  public:
  22   HistogramSamples();
  23   virtual ~HistogramSamples();
  24
  25   virtual void Accumulate(HistogramBase::Sample value,
  26                           HistogramBase::Count count) = 0;
  27   virtual HistogramBase::Count GetCount(HistogramBase::Sample value) const = 0;
  28   virtual HistogramBase::Count TotalCount() const = 0;
  29
  30   virtual void Add(const HistogramSamples& other);
  31
  32   // Add from serialized samples.
  33   virtual bool AddFromPickle(PickleIterator* iter);
  34
  35   virtual void Subtract(const HistogramSamples& other);
  36
  37   virtual scoped_ptr<SampleCountIterator> Iterator() const = 0;
  38   virtual bool Serialize(Pickle* pickle) const;
  39
  40   // Accessor fuctions.
  41   int64 sum() const { return sum_; }
  42   HistogramBase::Count redundant_count() const {
  43     return subtle::NoBarrier_Load(&redundant_count_);
  44   }
  45
  46  protected:
  47   // Based on |op| type, add or subtract sample counts data from the iterator.
  48   enum Operator { ADD, SUBTRACT };
  49   virtual bool AddSubtractImpl(SampleCountIterator* iter, Operator op) = 0;
  50
  51   void IncreaseSum(int64 diff);
  52   void IncreaseRedundantCount(HistogramBase::Count diff);
  53
  54  private:
  55   int64 sum_;
  56
  57   // |redundant_count_| helps identify memory corruption. It redundantly stores
  58   // the total number of samples accumulated in the histogram. We can compare
  59   // this count to the sum of the counts (TotalCount() function), and detect
  60   // problems. Note, depending on the implementation of different histogram
  61   // types, there might be races during histogram accumulation and snapshotting
  62   // that we choose to accept. In this case, the tallies might mismatch even
  63   // when no memory corruption has happened.
  64   HistogramBase::AtomicCount redundant_count_;
  65 };
  66
  67 class BASE_EXPORT SampleCountIterator {
  68  public:
  69   virtual ~SampleCountIterator();
  70
  71   virtual bool Done() const = 0;
  72   virtual void Next() = 0;
  73
  74   // Get the sample and count at current position.
  75   // |min| |max| and |count| can be NULL if the value is not of interest.
  76   // Requires: !Done();
  77   virtual void Get(HistogramBase::Sample* min,
  78                    HistogramBase::Sample* max,
  79                    HistogramBase::Count* count) const = 0;
  80
  81   // Get the index of current histogram bucket.
  82   // For histograms that don't use predefined buckets, it returns false.
  83   // Requires: !Done();
  84   virtual bool GetBucketIndex(size_t* index) const;
  85 };
  86
  87 }  // namespace base
  88
  89 #endif  // BASE_METRICS_HISTOGRAM_SAMPLES_H_