Add SampleMap and use it in SparseHistogram

base/metrics/sample_map.cc

+// 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;

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

nit: would using work here?

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

nope... using only works for namespace

+typedef HistogramBase::Sample Sample;
+
+SampleMap::SampleMap() {}
+
+SampleMap::~SampleMap() {}
+
+void SampleMap::Accumulate(Sample value, Count count) {
+  base::AutoLock auto_lock(lock_);
+  sample_counts_[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_counts_.find(value);
+  if (it == sample_counts_.end())
+    return 0;
+  return it->second;
+}
+
+Count SampleMap::TotalCount() const {
+  Count count = 0;
+
+  base::AutoLock auto_lock(lock_);
+  for (map<Sample, Count>::const_iterator it = sample_counts_.begin();
+       it != sample_counts_.end();
+       ++it) {
+    count += it->second;
+  }
+  return count;
+}
+
+scoped_ptr<SampleCountIterator> SampleMap::Iterator() const {
+  return scoped_ptr<SampleCountIterator>(new SampleMapIterator(sample_counts_));
+}
+
+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.
+    sample_counts_[min] +=
+        (instruction ==  HistogramSamples::ADD) ? count : -count;
+  }
+  return true;
+}
+
+SampleMapIterator::SampleMapIterator(const map<Sample, Count>& sample_counts)
+    : iter_(sample_counts.begin()),
+      end_(sample_counts.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());

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

I'm surprised we're not holding a lock when we access the map.

We especially need a lock when snapshotting.

I'd suggest that the constructor should do the snapshotting.

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

As discussed locked in SnapshotSamples function

+  if (min != NULL)
+    *min = iter_->first;
+  if (max != NULL)
+    *max = iter_->first + 1;
+  if (count != NULL)
+    *count = iter_->second;
+}
+
+}  // namespace base