Fixed the racing in the resampler of webrtc when two streams are calling OnData()

content/renderer/media/webrtc_audio_device_impl.cc

 // Copyright 2013 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 "content/renderer/media/webrtc_audio_device_impl.h"
 
 #include "base/bind.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_util.h"
 #include "base/win/windows_version.h"
@@ skipping 63 matching lines @@
   }
 
   // Write audio samples in blocks of 10 milliseconds to the registered
   // webrtc::AudioTransport sink. Keep writing until our internal byte
   // buffer is empty.
   const int16* audio_buffer = audio_data;
   const int samples_per_10_msec = (sample_rate / 100);
   CHECK_EQ(number_of_frames % samples_per_10_msec, 0);
   int accumulated_audio_samples = 0;
   uint32_t new_volume = 0;
+
+  // The lock here is to protect the racing in the resampler inside webrtc when
+  // there are more than one input stream calling OnData(), which can happen
+  // when the users setup two getUserMedia, one for the microphone, another
+  // for WebAudio. Currently we don't have a better way to fix it except for
+  // adding a lock here to sequence the call.
+  // TODO(xians): Remove this workaround after we move the
+  // webrtc::AudioProcessing module to Chrome. See http://crbug/264611 for
+  // details.
+  base::AutoLock auto_lock(capture_callback_lock_);
   while (accumulated_audio_samples < number_of_frames) {
     // Deliver 10ms of recorded 16-bit linear PCM audio.
     int new_mic_level = audio_transport_callback_->OnDataAvailable(
         &channels[0],
         channels.size(),
         audio_buffer,
         sample_rate,
         number_of_channels,
         samples_per_10_msec,
         total_delay_ms,
@@ skipping 346 matching lines @@
   for (CapturerList::const_iterator iter = capturers_.begin();
        iter != capturers_.end(); ++iter) {
     if (!(*iter)->device_id().empty())
       return *iter;
   }
 
   return NULL;
 }
 
 }  // namespace content