Add lock to fix race in AudioRendererMixerInput.

media/base/audio_renderer_mixer_input.h

 // 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.
 
 #ifndef MEDIA_BASE_AUDIO_RENDERER_MIXER_INPUT_H_
 #define MEDIA_BASE_AUDIO_RENDERER_MIXER_INPUT_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/synchronization/lock.h"
 #include "media/base/audio_converter.h"
 #include "media/base/audio_renderer_sink.h"
 #include "media/base/output_device.h"
 #include "url/origin.h"
 
 namespace media {
 
 class AudioRendererMixer;
 
 class MEDIA_EXPORT AudioRendererMixerInput
@@ skipping 40 matching lines @@
 
   // Called by AudioRendererMixer when an error occurs.
   void OnRenderError();
 
  protected:
   ~AudioRendererMixerInput() override;
 
  private:
   friend class AudioRendererMixerInputTest;
 
+  // AudioConverter::InputCallback implementation.
+  double ProvideInput(AudioBus* audio_bus,
+                      base::TimeDelta buffer_delay) override;
+
+  // The implementation for these methods is split out to avoid re-entrant
+  // locking when called by multiple internal callers. Re-entrant locking is
+  // not supported with base::Lock.
+  void Stop_Locked();
+  void Play_Locked();
+  void Pause_Locked();
+  void SwitchOutputDevice_Locked(const std::string& device_id,
+                                 const url::Origin& security_origin,
+                                 const SwitchOutputDeviceCB& callback);
+
+  // This class is used by both media thread (e.g. SetVolume) and audio device
+  // thread (e.g. ProvideInput).
+  base::Lock lock_;
+
+  // ---------------[ All variables below protected by |lock_| ]---------------
+
   bool started_;
   bool playing_;
   double volume_;
 
-  // AudioConverter::InputCallback implementation.
-  double ProvideInput(AudioBus* audio_bus,
-                      base::TimeDelta buffer_delay) override;
 
   // Callbacks provided during construction which allow AudioRendererMixerInput
   // to retrieve a mixer during Initialize() and notify when it's done with it.
   const GetMixerCB get_mixer_cb_;
   const RemoveMixerCB remove_mixer_cb_;
 
   // Callbacks provided during construction which allows AudioRendererMixerInput
   // to access hardware output parameters when it is detached from the mixer.
   const GetHardwareParamsCB get_hardware_params_cb_;
 
@@ skipping 19 matching lines @@
   SwitchOutputDeviceCB pending_switch_callback_;
   std::string pending_switch_device_id_;
   url::Origin pending_switch_security_origin_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerInput);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_INPUT_H_