Add SampleMap and use it in SparseHistogram

base/metrics/sample_map.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.
+
+// SampleMap implements HistogramSamples interface. It is used by the
+// SparseHistogram class to store samples.
+
+#ifndef BASE_METRICS_SAMPLE_MAP_H_
+#define BASE_METRICS_SAMPLE_MAP_H_
+
+#include <map>
+
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/synchronization/lock.h"
+
+namespace base {
+
+class BASE_EXPORT_PRIVATE SampleMap : public HistogramSamples {
+ public:
+  SampleMap();
+  virtual ~SampleMap();
+
+  // HistogramSamples implementation:
+  virtual void Accumulate(HistogramBase::Sample value,
+                          HistogramBase::Count count) OVERRIDE;
+  virtual HistogramBase::Count GetCount(
+      HistogramBase::Sample value) const OVERRIDE;
+  virtual HistogramBase::Count TotalCount() const OVERRIDE;
+  virtual scoped_ptr<SampleCountIterator> Iterator() const OVERRIDE;
+
+ protected:
+  virtual bool AddSubtractImpl(
+      SampleCountIterator* iter,
+      HistogramSamples::Instruction instruction) OVERRIDE;
+
+ private:
+  std::map<HistogramBase::Sample, HistogramBase::Count> sample_counts_;
+
+  // Protects access to above map.
+  mutable base::Lock lock_;
+
+  friend class SparseHistogram;  // To lock its samples for snapshotting.
+
+  DISALLOW_COPY_AND_ASSIGN(SampleMap);
+};
+
+class BASE_EXPORT_PRIVATE SampleMapIterator : public SampleCountIterator {
+ public:
+  SampleMapIterator(
+      const std::map<HistogramBase::Sample, HistogramBase::Count>&
+          sample_counts);
+
+  virtual ~SampleMapIterator();
+
+  // SampleCountIterator implementation:
+  virtual bool Done() const OVERRIDE;
+  virtual void Next() OVERRIDE;
+  virtual void Get(HistogramBase::Sample* min,
+                   HistogramBase::Sample* max,
+                   HistogramBase::Count* count) const OVERRIDE;
+ private:
+  std::map<HistogramBase::Sample, HistogramBase::Count>::const_iterator iter_;
+  const std::map<HistogramBase::Sample, HistogramBase::Count>::const_iterator

[jar (doing other things), 2012/10/02 17:41:11]

This seems like an implementation detail (a shortcut in fact), that is best
placed in the implementation file, possibly in an anonymous namespace. 

Putting it here just complicates reading... but seems to add no value.

+      end_;
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_SAMPLE_MAP_H_