Reorganize histograms for persistence.

base/metrics/sample_vector.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.
 
 // SampleVector implements HistogramSamples interface. It is used by all
 // Histogram based classes to store samples.
 
 #ifndef BASE_METRICS_SAMPLE_VECTOR_H_
 #define BASE_METRICS_SAMPLE_VECTOR_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_samples.h"
 
 namespace base {
 
 class BucketRanges;
 
 class BASE_EXPORT SampleVector : public HistogramSamples {
  public:
   explicit SampleVector(const BucketRanges* bucket_ranges);
+  SampleVector(uint64 id, const BucketRanges* bucket_ranges);
+  SampleVector(uint64 id,
+               HistogramBase::AtomicCount* counts,
+               size_t counts_size,
+               Metadata* meta,
+               const BucketRanges* bucket_ranges);
   ~SampleVector() override;
 
   // HistogramSamples implementation:
   void Accumulate(HistogramBase::Sample value,
                   HistogramBase::Count count) override;
   HistogramBase::Count GetCount(HistogramBase::Sample value) const override;
   HistogramBase::Count TotalCount() const override;
   scoped_ptr<SampleCountIterator> Iterator() const override;
 
   // Get count of a specific bucket.
   HistogramBase::Count GetCountAtIndex(size_t bucket_index) const;
 
  protected:
   bool AddSubtractImpl(
       SampleCountIterator* iter,
       HistogramSamples::Operator op) override;  // |op| is ADD or SUBTRACT.
 
   virtual size_t GetBucketIndex(HistogramBase::Sample value) const;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(HistogramTest, CorruptSampleCounts);
 
-  std::vector<HistogramBase::AtomicCount> counts_;
+  // In the case where this class manages the memory, here it is.
+  std::vector<HistogramBase::AtomicCount> local_counts_;
+
+  // These are raw pointers rather than objects for flexibility. The actual
+  // memory is either managed by local_counts_ above or by an external object
+  // and passed in directly.
+  HistogramBase::AtomicCount* counts_;
+  size_t counts_size_;
 
   // Shares the same BucketRanges with Histogram object.
   const BucketRanges* const bucket_ranges_;
 
   DISALLOW_COPY_AND_ASSIGN(SampleVector);
 };
 
 class BASE_EXPORT SampleVectorIterator : public SampleCountIterator {
  public:
   SampleVectorIterator(const std::vector<HistogramBase::AtomicCount>* counts,
                        const BucketRanges* bucket_ranges);
+  SampleVectorIterator(const HistogramBase::AtomicCount* counts,
+                       size_t counts_size,
+                       const BucketRanges* bucket_ranges);
   ~SampleVectorIterator() override;
 
   // SampleCountIterator implementation:
   bool Done() const override;
   void Next() override;
   void Get(HistogramBase::Sample* min,
            HistogramBase::Sample* max,
            HistogramBase::Count* count) const override;
 
   // SampleVector uses predefined buckets, so iterator can return bucket index.
   bool GetBucketIndex(size_t* index) const override;
 
  private:
   void SkipEmptyBuckets();
 
-  const std::vector<HistogramBase::AtomicCount>* counts_;
+  const HistogramBase::AtomicCount* counts_;

[Alexei Svitkine (slow), 2015/12/01 16:32:14]

Can this be "const HistogramBase::AtomicCount* const" counts ? i.e. the pointer
doesn't change after ctor call. Same for bucket_ranges.

+  size_t counts_size_;

[Alexei Svitkine (slow), 2015/12/01 16:32:14]

Make this const

   const BucketRanges* bucket_ranges_;
 
   size_t index_;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_SAMPLE_VECTOR_H_