Use swap instead of copy in RtcHistogram::GetAndReset.

webrtc/system_wrappers/source/metrics_default.cc

 // Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the LICENSE file in the root of the source
 // tree. An additional intellectual property rights grant can be found
 // in the file PATENTS.  All contributing project authors may
 // be found in the AUTHORS file in the root of the source tree.
 //
 
 #include "webrtc/system_wrappers/include/metrics_default.h"
 
+#include <algorithm>
+
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/system_wrappers/include/metrics.h"
 
 // Default implementation of histogram methods for WebRTC clients that do not
 // want to provide their own implementation.
 
 namespace webrtc {
 namespace metrics {
 class Histogram;
 
 namespace {
 // Limit for the maximum number of sample values that can be stored.
 // TODO(asapersson): Consider using bucket count (and set up
 // linearly/exponentially spaced buckets) if samples are logged more frequently.
 const int kMaxSampleMapSize = 300;
 
 class RtcHistogram {
  public:
   RtcHistogram(const std::string& name, int min, int max, int bucket_count)
       : min_(min), max_(max), info_(name, min, max, bucket_count) {
     RTC_DCHECK_GT(bucket_count, 0);
   }
 
   void Add(int sample) {
-    if (sample < min_)
-      sample = min_ - 1;  // Underflow bucket.
-    if (sample > max_)
-      sample = max_;
+    sample = std::min(sample, max_);
+    sample = std::max(sample, min_ - 1);  // Underflow bucket.
 
     rtc::CritScope cs(&crit_);
     if (info_.samples.size() == kMaxSampleMapSize &&
         info_.samples.find(sample) == info_.samples.end()) {
       return;
     }
     ++info_.samples[sample];
   }
 
   // Returns a copy (or nullptr if there are no samples) and clears samples.
   std::unique_ptr<SampleInfo> GetAndReset() {
     rtc::CritScope cs(&crit_);
     if (info_.samples.empty())
       return nullptr;
 
     SampleInfo* copy =
         new SampleInfo(info_.name, info_.min, info_.max, info_.bucket_count);
-    copy->samples = info_.samples;
-    info_.samples.clear();
+
+    std::swap(info_.samples, copy->samples);

[stefan-webrtc, 2016/11/28 15:15:55]

Should we clear info_.samples after this?

[åsapersson, 2016/11/29 14:22:21]

copy->samples has an empty map before the swap.

[stefan-webrtc, 2016/11/29 16:15:53]

Acknowledged.

+
     return std::unique_ptr<SampleInfo>(copy);
   }
 
   const std::string& name() const { return info_.name; }
 
   // Functions only for testing.
   void Reset() {
     rtc::CritScope cs(&crit_);
     info_.samples.clear();
   }
@@ skipping 214 matching lines @@
   return map ? map->NumSamples(name) : 0;
 }
 
 int MinSample(const std::string& name) {
   RtcHistogramMap* map = GetMap();
   return map ? map->MinSample(name) : -1;
 }
 
 }  // namespace metrics
 }  // namespace webrtc