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