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      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_
     90