Elimiteted race condition in the AudioMixer.

webrtc/modules/audio_mixer/audio_mixer_impl.cc

 /*
  *  Copyright (c) 2012 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.
  */
 
@@ skipping 182 matching lines @@
   RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
 
   if (OutputFrequency() != sample_rate) {
     SetOutputFrequency(sample_rate);
   }
 
   AudioFrameList mix_list;
   {
     rtc::CritScope lock(&crit_);
     mix_list = GetAudioFromSources();
+
+    for (const auto& frame : mix_list) {
+      RemixFrame(number_of_channels, frame);
+    }
+
+    audio_frame_for_mixing->UpdateFrame(
+        -1, time_stamp_, NULL, 0, OutputFrequency(), AudioFrame::kNormalSpeech,
+        AudioFrame::kVadPassive, number_of_channels);
+
+    time_stamp_ += static_cast<uint32_t>(sample_size_);
+
+    use_limiter_ = mix_list.size() > 1;
+
+    // We only use the limiter if we're actually mixing multiple streams.
+    MixFromList(audio_frame_for_mixing, mix_list, use_limiter_);
   }
 
-  for (const auto& frame : mix_list) {
-    RemixFrame(number_of_channels, frame);
-  }
-
-  audio_frame_for_mixing->UpdateFrame(
-      -1, time_stamp_, NULL, 0, OutputFrequency(), AudioFrame::kNormalSpeech,
-      AudioFrame::kVadPassive, number_of_channels);
-
-  time_stamp_ += static_cast<uint32_t>(sample_size_);
-
-  use_limiter_ = mix_list.size() > 1;
-
-  // We only use the limiter if we're actually mixing multiple streams.
-  MixFromList(audio_frame_for_mixing, mix_list, use_limiter_);
-
   if (audio_frame_for_mixing->samples_per_channel_ == 0) {
     // Nothing was mixed, set the audio samples to silence.
     audio_frame_for_mixing->samples_per_channel_ = sample_size_;
     audio_frame_for_mixing->Mute();
   } else {
     // Only call the limiter if we have something to mix.
     LimitMixedAudio(audio_frame_for_mixing);
   }
 
   return;
@@ skipping 115 matching lines @@
 
   const auto iter = FindSourceInList(audio_source, &audio_source_list_);
   if (iter != audio_source_list_.end()) {
     return (*iter)->is_mixed;
   }
 
   LOG(LS_ERROR) << "Audio source unknown";
   return false;
 }
 }  // namespace webrtc