base/metrics/bucket_ranges.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 // BucketRanges stores the vector of ranges that delimit what samples are
   6 // tallied in the corresponding buckets of a histogram. Histograms that have
   7 // same ranges for all their corresponding buckets should share the same
   8 // BucketRanges object.
   9 //
  10 // E.g. A 5 buckets LinearHistogram with 1 as minimal value and 4 as maximal
  11 // value will need a BucketRanges with 6 ranges:
  12 // 0, 1, 2, 3, 4, INT_MAX
  13 //
  14 // TODO(kaiwang): Currently we keep all negative values in 0~1 bucket. Consider
  15 // changing 0 to INT_MIN.
  16
  17 #ifndef BASE_METRICS_BUCKET_RANGES_H_
  18 #define BASE_METRICS_BUCKET_RANGES_H_
  19
  20 #include <vector>
  21
  22 #include "base/base_export.h"
  23 #include "base/basictypes.h"
  24 #include "base/gtest_prod_util.h"
  25 #include "base/metrics/histogram_base.h"
  26
  27 namespace base {
  28
  29 class BASE_EXPORT BucketRanges {
  30  public:
  31   typedef std::vector<HistogramBase::Sample> Ranges;
  32
  33   explicit BucketRanges(size_t num_ranges);
  34   ~BucketRanges();
  35
  36   size_t size() const { return ranges_.size(); }
  37   HistogramBase::Sample range(size_t i) const { return ranges_[i]; }
  38   void set_range(size_t i, HistogramBase::Sample value);
  39   uint32 checksum() const { return checksum_; }
  40   void set_checksum(uint32 checksum) { checksum_ = checksum; }
  41
  42   // A bucket is defined by a consecutive pair of entries in |ranges|, so there
  43   // is one fewer bucket than there are ranges.  For example, if |ranges| is
  44   // [0, 1, 3, 7, INT_MAX], then the buckets in this histogram are
  45   // [0, 1), [1, 3), [3, 7), and [7, INT_MAX).
  46   size_t bucket_count() const { return ranges_.size() - 1; }
  47
  48   // Checksum methods to verify whether the ranges are corrupted (e.g. bad
  49   // memory access).
  50   uint32 CalculateChecksum() const;
  51   bool HasValidChecksum() const;
  52   void ResetChecksum();
  53
  54   // Return true iff |other| object has same ranges_ as |this| object's ranges_.
  55   bool Equals(const BucketRanges* other) const;
  56
  57  private:
  58   // A monotonically increasing list of values which determine which bucket to
  59   // put a sample into.  For each index, show the smallest sample that can be
  60   // added to the corresponding bucket.
  61   Ranges ranges_;
  62
  63   // Checksum for the conntents of ranges_.  Used to detect random over-writes
  64   // of our data, and to quickly see if some other BucketRanges instance is
  65   // possibly Equal() to this instance.
  66   // TODO(kaiwang): Consider change this to uint64. Because we see a lot of
  67   // noise on UMA dashboard.
  68   uint32 checksum_;
  69
  70   DISALLOW_COPY_AND_ASSIGN(BucketRanges);
  71 };
  72
  73 //////////////////////////////////////////////////////////////////////////////
  74 // Expose only for test.
  75 BASE_EXPORT_PRIVATE extern const uint32 kCrcTable[256];
  76
  77 }  // namespace base
  78
  79 #endif  // BASE_METRICS_BUCKET_RANGES_H_