Support "shared" histograms between processes.

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 179 matching lines @@
   void WriteAscii(std::string* output) const override;
 
  protected:
   // |ranges| should contain the underflow and overflow buckets. See top
   // comments for example.
   Histogram(const std::string& name,
             Sample minimum,
             Sample maximum,
             const BucketRanges* ranges);
 
+  // Traditionally, histograms allocate their own memory for the bucket
+  // 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,
+            size_t counts_size,
+            HistogramSamples::Metadata* 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(size_t index) const;
 
   // Get normalized size, relative to the ranges(i).
   virtual double GetBucketSize(Count current, size_t i) const;
 
   // Return a string description of what goes in a given bucket.
   // Most commonly this is the numeric value, but in derived classes it may
   // be a name (or string description) given to the bucket.
   virtual const std::string GetAsciiBucketRange(size_t it) const;
 
  private:
   // Allow tests to corrupt our innards for testing purposes.
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, BoundsTest);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, BucketPlacementTest);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptBucketBounds);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptSampleCounts);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, NameMatchTest);
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, AddCountTest);
 
   friend class StatisticsRecorder;  // To allow it to delete duplicates.
   friend class StatisticsRecorderTest;
 
+  friend BASE_EXPORT HistogramBase* HistogramBase::CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   // Implementation of SnapshotSamples function.
   scoped_ptr<SampleVector> SnapshotSampleVector() const;
 
   //----------------------------------------------------------------------------
   // Helpers for emitting Ascii graphic.  Each method appends data to output.
 
@@ skipping 94 matching lines @@
 
   // Overridden from Histogram:
   HistogramType GetHistogramType() const override;
 
  protected:
   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,
+                  size_t counts_size,
+                  HistogramSamples::Metadata* meta);
+
   double GetBucketSize(Count current, size_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(size_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(size_t index) const override;
 
  private:
+  friend BASE_EXPORT HistogramBase* HistogramBase::CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   // For some ranges, we store a printable description of a bucket range.
   // If there is no description, then GetAsciiBucketRange() uses parent class
   // to provide a description.
   typedef std::map<Sample, std::string> BucketDescriptionMap;
   BucketDescriptionMap bucket_description_;
 
   DISALLOW_COPY_AND_ASSIGN(LinearHistogram);
 };
 
 //------------------------------------------------------------------------------
 
 // BooleanHistogram is a histogram for booleans.
 class BASE_EXPORT BooleanHistogram : public LinearHistogram {
  public:
   static HistogramBase* FactoryGet(const std::string& name, int32 flags);
 
   // 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 flags);
 
   HistogramType GetHistogramType() const override;
 
  private:
   BooleanHistogram(const std::string& name, const BucketRanges* ranges);
+  BooleanHistogram(const std::string& name,
+                   const BucketRanges* ranges,
+                   HistogramBase::AtomicCount* counts,
+                   HistogramSamples::Metadata* meta);
 
+  friend BASE_EXPORT HistogramBase* HistogramBase::CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   DISALLOW_COPY_AND_ASSIGN(BooleanHistogram);
 };
 
 //------------------------------------------------------------------------------
 
 // CustomHistogram is a histogram for a set of custom integers.
@@ skipping 22 matching lines @@
   // 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,
                                                  size_t num_values);
  protected:
   CustomHistogram(const std::string& name,
                   const BucketRanges* ranges);
 
+  CustomHistogram(const std::string& name,
+                  const BucketRanges* ranges,
+                  HistogramBase::AtomicCount* counts,
+                  size_t counts_size,
+                  HistogramSamples::Metadata* meta);
+
   // HistogramBase implementation:
   bool SerializeInfoImpl(base::Pickle* pickle) const override;
 
   double GetBucketSize(Count current, size_t i) const override;
 
  private:
+  friend BASE_EXPORT HistogramBase* HistogramBase::CreatePersistentHistogram(
+      PersistentMemoryAllocator* allocator,
+      PersistentHistogramData* histogram_data);
   friend BASE_EXPORT HistogramBase* DeserializeHistogramInfo(
       base::PickleIterator* iter);
   static HistogramBase* DeserializeInfoImpl(base::PickleIterator* iter);
 
   static bool ValidateCustomRanges(const std::vector<Sample>& custom_ranges);
   static BucketRanges* CreateBucketRangesFromCustomRanges(
       const std::vector<Sample>& custom_ranges);
 
   DISALLOW_COPY_AND_ASSIGN(CustomHistogram);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_H_