Add SampleMap and use it in SparseHistogram

base/metrics/sample_map.cc

Index: base/metrics/sample_map.cc
diff --git a/base/metrics/sample_map.cc b/base/metrics/sample_map.cc
new file mode 100644
index 0000000000000000000000000000000000000000..9da8d23b0c140ab128921c3112c4eafe397113cf
--- /dev/null
+++ b/base/metrics/sample_map.cc
@@ -0,0 +1,94 @@
+// 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.
+
+#include "base/metrics/sample_map.h"
+
+#include "base/logging.h"
+
+using std::map;
+
+namespace base {
+
+typedef HistogramBase::Count Count;
+typedef HistogramBase::Sample Sample;
+
+SampleMap::SampleMap() {}
+
+SampleMap::~SampleMap() {}
+
+void SampleMap::Accumulate(Sample value, Count count) {
+  base::AutoLock auto_lock(lock_);
+  sample_count_[value] += count;
+  IncreaseSum(count * value);
+  IncreaseRedundantCount(count);
+}
+
+Count SampleMap::GetCount(Sample value) const {
+  base::AutoLock auto_lock(lock_);
+  map<Sample, Count>::const_iterator it = sample_count_.find(value);
+  if (it == sample_count_.end())
+    return 0;
+  return it->second;
+}
+
+Count SampleMap::TotalCount() const {
+  Count count = 0;
+  map<Sample, Count>::const_iterator it;

[Ilya Sherman, 2012/10/01 21:24:50]

nit: Please define this within the for loop's variable initialization clause --
this doesn't need to be scoped outside the loop.

[kaiwang, 2012/10/01 22:38:52]

Done.

+
+  base::AutoLock auto_lock(lock_);
+  for (it = sample_count_.begin(); it != sample_count_.end(); ++it) {
+    count += it->second;
+  }
+  return count;
+}
+
+scoped_ptr<SampleCountIterator> SampleMap::Iterator() const {
+  return scoped_ptr<SampleCountIterator>(new SampleMapIterator(sample_count_));
+}
+
+bool SampleMap::AddSubtractImpl(SampleCountIterator* iter,
+                                HistogramSamples::Instruction instruction) {
+  HistogramBase::Sample min;
+  HistogramBase::Sample max;
+  HistogramBase::Count count;
+
+  base::AutoLock auto_lock(lock_);
+  for (; !iter->Done(); iter->Next()) {
+    iter->Get(&min, &max, &count);
+    if (min + 1 != max)
+      return false;  // SparseHistogram only supports bucket with size 1.

[Ilya Sherman, 2012/10/01 21:24:50]

nit: Should this be a DCHECK?

[kaiwang, 2012/10/01 22:38:52]

As in SampleVector, this function can be called in different situations,
sometimes it's better to DCHECK, sometimes it's better to return some error
(e.g. parse histogram data from renderer).

+    sample_count_[min] +=
+        (instruction ==  HistogramSamples::ADD) ? count : -count;

[Ilya Sherman, 2012/10/01 21:24:50]

nit: I don't think you need the "HistogramSamples::" prefix, since this class
inherits from that one.

[kaiwang, 2012/10/01 22:38:52]

Right, but I think this is a bit easier for code reading. If the reader is
interested to know where ADD is defined, he will go to histogram_samples.h.
Without class name, ADD can be defined anywhere

+  }
+  return true;
+}
+
+SampleMapIterator::SampleMapIterator(const map<Sample, Count>& sample_count)
+    : iter_(sample_count.begin()),
+      end_(sample_count.end()) {}
+
+SampleMapIterator::~SampleMapIterator() {}
+
+bool SampleMapIterator::Done() const {
+  return iter_ == end_;
+}
+
+void SampleMapIterator::Next() {
+  DCHECK(!Done());
+  iter_++;
+}
+
+void SampleMapIterator::Get(HistogramBase::Sample* min,
+                            HistogramBase::Sample* max,
+                            HistogramBase::Count* count) const {
+  DCHECK(!Done());
+  if (min != NULL)
+    *min = iter_->first;
+  if (max != NULL)
+    *max = iter_->first + 1;
+  if (count != NULL)
+    *count = iter_->second;
+}
+
+}  // namespace base