Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram.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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 
 // It supports calls to accumulate either time intervals (which are processed
 // as integral number of milliseconds), or arbitrary integral units.
@@ skipping 127 matching lines @@
                                        base::TimeDelta maximum,
                                        uint32_t bucket_count,
                                        int32_t flags);
 
   // Get a histogram using data in persistent storage.
   static HistogramBase* PersistentGet(const std::string& name,
                                       Sample minimum,
                                       Sample maximum,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged_counts,
                                       uint32_t counts_size,
-                                      HistogramSamples::Metadata* meta);
+                                      HistogramSamples::Metadata* meta,
+                                      HistogramSamples::Metadata* logged_meta);
 
   static void InitializeBucketRanges(Sample minimum,
                                      Sample maximum,
                                      BucketRanges* ranges);
 
   // This constant if for FindCorruption. Since snapshots of histograms are
   // taken asynchronously relative to sampling, and our counting code currently
   // does not prevent race conditions, it is pretty likely that we'll catch a
   // redundant count that doesn't match the sample count.  We allow for a
   // certain amount of slop before flagging this as an inconsistency. Even with
   // an inconsistency, we'll snapshot it again (for UMA in about a half hour),
   // so we'll eventually get the data, if it was not the result of a corruption.
   static const int kCommonRaceBasedCountMismatch;
 
   // Check to see if bucket ranges, counts and tallies in the snapshot are
   // consistent with the bucket ranges and checksums in our histogram.  This can
   // produce a false-alarm if a race occurred in the reading of the data during
   // a SnapShot process, but should otherwise be false at all times (unless we
   // have memory over-writes, or DRAM failures).

[Alexei Svitkine (slow), 2016/02/17 16:21:12]

Nit: While here, can you point to the enum of flags this is returning in the
comment?

[bcwhite, 2016/02/17 17:58:20]

Done.

-  int FindCorruption(const HistogramSamples& samples) const override;
+  unsigned FindCorruption(const HistogramSamples& samples) const override;
 
   //----------------------------------------------------------------------------
   // Accessors for factory construction, serialization and testing.
   //----------------------------------------------------------------------------
   Sample declared_min() const { return declared_min_; }
   Sample declared_max() const { return declared_max_; }
   virtual Sample ranges(uint32_t i) const;
   virtual uint32_t bucket_count() const;
   const BucketRanges* bucket_ranges() const { return bucket_ranges_; }
 
@@ skipping 10 matching lines @@
 
   // HistogramBase implementation:
   uint64_t name_hash() const override;
   HistogramType GetHistogramType() const override;
   bool HasConstructionArguments(Sample expected_minimum,
                                 Sample expected_maximum,
                                 uint32_t expected_bucket_count) const override;
   void Add(Sample value) override;
   void AddCount(Sample value, int count) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const override;
+  scoped_ptr<HistogramSamples> SnapshotDelta() override;
   void AddSamples(const HistogramSamples& samples) override;
   bool AddSamplesFromPickle(base::PickleIterator* iter) override;
   void WriteHTMLGraph(std::string* output) const override;
   void WriteAscii(std::string* output) const override;
 
  protected:
   // This class, defined entirely within the .cc file, contains all the
   // common logic for building a Histogram and can be overridden by more
   // specific types to alter details of how the creation is done. It is
   // defined as an embedded class (rather than an anonymous one) so it
@@ skipping 11 matching lines @@
   // vector but "shared" histograms use memory regions allocated from a
   // special memory segment that is passed in here.  It is assumed that
   // the life of this memory is managed externally and exceeds the lifetime
   // of this object. Practically, this memory is never released until the
   // process exits and the OS cleans it up.
   Histogram(const std::string& name,
             Sample minimum,
             Sample maximum,
             const BucketRanges* ranges,
             HistogramBase::AtomicCount* counts,
+            HistogramBase::AtomicCount* logged_counts,
             uint32_t counts_size,
-            HistogramSamples::Metadata* meta);
+            HistogramSamples::Metadata* meta,
+            HistogramSamples::Metadata* logged_meta);
 
   ~Histogram() override;
 
   // HistogramBase implementation:
   bool SerializeInfoImpl(base::Pickle* pickle) const override;
 
   // Method to override to skip the display of the i'th bucket if it's empty.
   virtual bool PrintEmptyBucket(uint32_t index) const;
 
   // Get normalized size, relative to the ranges(i).
@@ skipping 53 matching lines @@
   // Does not own this object. Should get from StatisticsRecorder.
   const BucketRanges* bucket_ranges_;
 
   Sample declared_min_;  // Less than this goes into the first bucket.
   Sample declared_max_;  // Over this goes into the last bucket.
 
   // Finally, provide the state that changes with the addition of each new
   // sample.
   scoped_ptr<SampleVector> samples_;
 
+  // Also keep a previous uploaded state for calculating deltas.
+  scoped_ptr<HistogramSamples> logged_samples_;
+
   DISALLOW_COPY_AND_ASSIGN(Histogram);
 };
 
 //------------------------------------------------------------------------------
 
 // LinearHistogram is a more traditional histogram, with evenly spaced
 // buckets.
 class BASE_EXPORT LinearHistogram : public Histogram {
  public:
   ~LinearHistogram() override;
@@ skipping 24 matching lines @@
                                        TimeDelta maximum,
                                        uint32_t bucket_count,
                                        int32_t flags);
 
   // Get a histogram using data in persistent storage.
   static HistogramBase* PersistentGet(const std::string& name,
                                       Sample minimum,
                                       Sample maximum,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged_counts,
                                       uint32_t counts_size,
-                                      HistogramSamples::Metadata* meta);
+                                      HistogramSamples::Metadata* meta,
+                                      HistogramSamples::Metadata* logged_meta);
 
   struct DescriptionPair {
     Sample sample;
     const char* description;  // Null means end of a list of pairs.
   };
 
   // Create a LinearHistogram and store a list of number/text values for use in
   // writing the histogram graph.
   // |descriptions| can be NULL, which means no special descriptions to set. If
   // it's not NULL, the last element in the array must has a NULL in its
@@ skipping 19 matching lines @@
   LinearHistogram(const std::string& name,
                   Sample minimum,
                   Sample maximum,
                   const BucketRanges* ranges);
 
   LinearHistogram(const std::string& name,
                   Sample minimum,
                   Sample maximum,
                   const BucketRanges* ranges,
                   HistogramBase::AtomicCount* counts,
+                  HistogramBase::AtomicCount* logged_counts,
                   uint32_t counts_size,
-                  HistogramSamples::Metadata* meta);
+                  HistogramSamples::Metadata* meta,
+                  HistogramSamples::Metadata* logged_meta);
 
   double GetBucketSize(Count current, uint32_t i) const override;
 
   // If we have a description for a bucket, then return that.  Otherwise
   // let parent class provide a (numeric) description.
   const std::string GetAsciiBucketRange(uint32_t i) const override;
 
   // Skip printing of name for numeric range if we have a name (and if this is
   // an empty bucket).
   bool PrintEmptyBucket(uint32_t index) const override;
@@ skipping 21 matching lines @@
 
   // Overload of the above function that takes a const char* |name| param,
   // to avoid code bloat from the std::string constructor being inlined into
   // call sites.
   static HistogramBase* FactoryGet(const char* name, int32_t flags);
 
   // Get a histogram using data in persistent storage.
   static HistogramBase* PersistentGet(const std::string& name,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
-                                      HistogramSamples::Metadata* meta);
+                                      HistogramBase::AtomicCount* logged_counts,
+                                      HistogramSamples::Metadata* meta,
+                                      HistogramSamples::Metadata* logged_meta);
 
   HistogramType GetHistogramType() const override;
 
  protected:
   class Factory;
 
  private:
   BooleanHistogram(const std::string& name, const BucketRanges* ranges);
   BooleanHistogram(const std::string& name,
                    const BucketRanges* ranges,
                    HistogramBase::AtomicCount* counts,
-                   HistogramSamples::Metadata* meta);
+                   HistogramBase::AtomicCount* logged_counts,
+                   HistogramSamples::Metadata* meta,
+                   HistogramSamples::Metadata* logged_meta);
 
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   DISALLOW_COPY_AND_ASSIGN(BooleanHistogram);
 };
 
 //------------------------------------------------------------------------------
 
@@ skipping 12 matching lines @@
   // to avoid code bloat from the std::string constructor being inlined into
   // call sites.
   static HistogramBase* FactoryGet(const char* name,
                                    const std::vector<Sample>& custom_ranges,
                                    int32_t flags);
 
   // Get a histogram using data in persistent storage.
   static HistogramBase* PersistentGet(const std::string& name,
                                       const BucketRanges* ranges,
                                       HistogramBase::AtomicCount* counts,
+                                      HistogramBase::AtomicCount* logged_counts,
                                       uint32_t counts_size,
-                                      HistogramSamples::Metadata* meta);
+                                      HistogramSamples::Metadata* meta,
+                                      HistogramSamples::Metadata* logged_meta);
 
   // Overridden from Histogram:
   HistogramType GetHistogramType() const override;
 
   // Helper method for transforming an array of valid enumeration values
   // to the std::vector<int> expected by UMA_HISTOGRAM_CUSTOM_ENUMERATION.
   // This function ensures that a guard bucket exists right after any
   // valid sample value (unless the next higher sample is also a valid value),
   // so that invalid samples never fall into the same bucket as valid samples.
   // TODO(kaiwang): Change name to ArrayToCustomEnumRanges.
   static std::vector<Sample> ArrayToCustomRanges(const Sample* values,
                                                  uint32_t num_values);
  protected:
   class Factory;
 
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges);
 
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges,
                   HistogramBase::AtomicCount* counts,
+                  HistogramBase::AtomicCount* logged_counts,
                   uint32_t counts_size,
-                  HistogramSamples::Metadata* meta);
+                  HistogramSamples::Metadata* meta,
+                  HistogramSamples::Metadata* logged_meta);
 
   // HistogramBase implementation:
   bool SerializeInfoImpl(base::Pickle* pickle) const override;
 
   double GetBucketSize(Count current, uint32_t i) const override;
 
  private:
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_