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 74 matching lines @@
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class BooleanHistogram;
 class CustomHistogram;
 class Histogram;
 class LinearHistogram;
+class PersistentMemoryAllocator;
 class Pickle;
 class PickleIterator;
 class SampleVector;
 
 class BASE_EXPORT Histogram : public HistogramBase {
  public:
   // Initialize maximum number of buckets in histograms as 16,384.
   static const size_t kBucketCount_MAX;
 
   typedef std::vector<Count> Counts;
@@ skipping 26 matching lines @@
                                    Sample minimum,
                                    Sample maximum,
                                    size_t bucket_count,
                                    int32_t flags);
   static HistogramBase* FactoryTimeGet(const char* name,
                                        base::TimeDelta minimum,
                                        base::TimeDelta maximum,
                                        size_t bucket_count,
                                        int32_t flags);
 
+  static HistogramBase* PersistentGet(const char* name,

[Alexei Svitkine (slow), 2016/01/12 21:54:44]

Add a comment, please.

[bcwhite, 2016/01/13 13:38:29]

Done.

+                                      Sample minimum,
+                                      Sample maximum,
+                                      const BucketRanges* ranges,
+                                      HistogramBase::AtomicCount* counts,
+                                      size_t counts_size,
+                                      HistogramSamples::Metadata* 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),
@@ skipping 35 matching lines @@
                                 size_t expected_bucket_count) const override;
   void Add(Sample value) override;
   void AddCount(Sample value, int count) override;
   scoped_ptr<HistogramSamples> SnapshotSamples() const 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
+  // can access the protected constructors.
+  class Factory;
+
   // |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;
@@ skipping 93 matching lines @@
                                    Sample minimum,
                                    Sample maximum,
                                    size_t bucket_count,
                                    int32_t flags);
   static HistogramBase* FactoryTimeGet(const char* name,
                                        TimeDelta minimum,
                                        TimeDelta maximum,
                                        size_t bucket_count,
                                        int32_t flags);
 
+  static HistogramBase* PersistentGet(const char* name,
+                                      Sample minimum,
+                                      Sample maximum,
+                                      const BucketRanges* ranges,
+                                      HistogramBase::AtomicCount* counts,
+                                      size_t counts_size,
+                                      HistogramSamples::Metadata* 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
   // "description" field.
   static HistogramBase* FactoryGetWithRangeDescription(
       const std::string& name,
       Sample minimum,
       Sample maximum,
       size_t bucket_count,
       int32_t flags,
       const DescriptionPair descriptions[]);
 
   static void InitializeBucketRanges(Sample minimum,
                                      Sample maximum,
                                      BucketRanges* ranges);
 
   // Overridden from Histogram:
   HistogramType GetHistogramType() const override;
 
  protected:
+  class Factory;
+
   LinearHistogram(const std::string& name,
                   Sample minimum,
                   Sample maximum,
                   const BucketRanges* ranges);
 
+  LinearHistogram(const std::string& name,

[Alexei Svitkine (slow), 2016/01/12 21:54:44]

Please add a comment to these extra constructors.

[bcwhite, 2016/01/13 13:38:29]

There's one big descriptive comment for the one in Histogram.  I left it out
here (and below) because the preceding ctor also had its comment omitted.

+                  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;
 
@@ skipping 16 matching lines @@
 // BooleanHistogram is a histogram for booleans.
 class BASE_EXPORT BooleanHistogram : public LinearHistogram {
  public:
   static HistogramBase* FactoryGet(const std::string& name, int32_t 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_t flags);
 
+  static HistogramBase* PersistentGet(const char* name,
+                                      const BucketRanges* ranges,
+                                      HistogramBase::AtomicCount* counts,
+                                      HistogramSamples::Metadata* 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);
 
   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.
 class BASE_EXPORT CustomHistogram : public Histogram {
  public:
   // |custom_ranges| contains a vector of limits on ranges. Each limit should be
   // > 0 and < kSampleType_MAX. (Currently 0 is still accepted for backward
   // compatibility). The limits can be unordered or contain duplication, but
   // client should not depend on this.
   static HistogramBase* FactoryGet(const std::string& name,
                                    const std::vector<Sample>& custom_ranges,
                                    int32_t 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,
                                    const std::vector<Sample>& custom_ranges,
                                    int32_t flags);
 
+  static HistogramBase* PersistentGet(const char* name,
+                                      const BucketRanges* ranges,
+                                      HistogramBase::AtomicCount* counts,
+                                      size_t counts_size,
+                                      HistogramSamples::Metadata* 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,
                                                  size_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,
+                  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* 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_