Fix a race condition in MediaStreamAudioTrackHost.

content/renderer/pepper/pepper_media_stream_audio_track_host.h

 // Copyright 2014 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.
 
 #ifndef CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
 #define CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_
 
 #include <deque>
 
 #include "base/compiler_specific.h"
@@ skipping 36 matching lines @@
     // This function is called on the main thread.
     void Configure(int32_t number_of_buffers);
 
    private:
     // Initializes buffers on the main thread.
     void SetFormatOnMainThread(int bytes_per_second);
 
     void InitBuffers();
 
     // Send enqueue buffer message on the main thread.
-    void SendEnqueueBufferMessageOnMainThread(int32_t index);
+    void SendEnqueueBufferMessageOnMainThread(int32_t index,
+                                              int32_t buffers_init_count);
 
     // MediaStreamAudioSink overrides:
     // These two functions should be called on the audio thread.
     virtual void OnData(const int16* audio_data,
                         int sample_rate,
                         int number_of_channels,
                         int number_of_frames) OVERRIDE;
     virtual void OnSetFormat(const media::AudioParameters& params) OVERRIDE;
 
     // Unowned host which is available during the AudioSink's lifespan.
@@ skipping 17 matching lines @@
 
     // The original audio parameters which is set in the first time of
     // OnSetFormat being called.
     // Access only on the audio thread.
     media::AudioParameters original_audio_params_;
 
     // The audio data size of one audio buffer in bytes.
     // Access only on the audio thread.
     uint32_t buffer_data_size_;
 
-    // A lock to protect the index queue |buffers_|.
+    // A lock to protect the index queue |buffers_|, |init_buffers_count_| and
+    // buffers in |host_->buffer_manager()|.
     base::Lock lock_;
 
     // A queue for free buffer indices.
     std::deque<int32_t> buffers_;
 
+    // Count of |InitBuffers()| calls.
+    int32_t init_buffers_count_;

[Anand Mistry (off Chromium), 2014/07/25 00:42:54]

To me, after reading the code, I think it would be clearer to call this
buffer_generation_ instead (or something like that).

[Peng, 2014/07/25 15:25:31]

Done.

+
     scoped_refptr<base::MessageLoopProxy> main_message_loop_proxy_;
 
     base::ThreadChecker audio_thread_checker_;
 
     base::WeakPtrFactory<AudioSink> weak_factory_;
 
     // Number of buffers.
     int32_t number_of_buffers_;
 
     // Number of bytes per second.
@@ skipping 30 matching lines @@
   bool connected_;
 
   AudioSink audio_sink_;
 
   DISALLOW_COPY_AND_ASSIGN(PepperMediaStreamAudioTrackHost);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_PEPPER_PEPPER_MEDIA_STREAM_AUDIO_TRACK_HOST_H_