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_;

[jar (doing other things), 2012/10/01 23:10:38]

nit: I'd prefer to see a typedef... as this map name is long, and makes lines
hard to read... and wrap.

It would get used 4 times in this file.

Possible names:
SampleCountsMap

[kaiwang, 2012/10/02 02:57:56]

Seems there's no way to make it a private typedef here, because it's used in
constructor.

I think the best solution might be moving Sample and Count to base

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

Moving Sample and Count SGTM. It will surely help with this long type.

Should we really move all of histograms to a base::metrics namespace?  This
would match the (current) directory structure, and avoid polluting the base::
namespace.

On 2012/10/02 02:57:56, kaiwang wrote:

+
+  // Protects access to above map.
+  mutable base::Lock lock_;
+
+  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
+      end_;
+};
+
+}  // namespace base
+
+#endif  // BASE_METRICS_SAMPLE_MAP_H_