Rejigger audio capture pipeline to work with separate main+worker threads (Mac).

media/audio/virtual_audio_input_stream.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_AUDIO_VIRTUAL_AUDIO_INPUT_STREAM_H_
 #define MEDIA_AUDIO_VIRTUAL_AUDIO_INPUT_STREAM_H_
 
 #include <map>
 #include <set>
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
 #include "media/audio/fake_audio_consumer.h"
 #include "media/base/audio_converter.h"
 
 namespace base {
 class MessageLoopProxy;
 }
 
 namespace media {
 
 class LoopbackAudioConverter;
 class VirtualAudioOutputStream;
 
 // VirtualAudioInputStream converts and mixes audio from attached
 // VirtualAudioOutputStreams into a single stream. It will continuously render
 // audio until this VirtualAudioInputStream is stopped and closed.
 class MEDIA_EXPORT VirtualAudioInputStream : public AudioInputStream {
  public:
   // Callback invoked just after VirtualAudioInputStream is closed.
   typedef base::Callback<void(VirtualAudioInputStream* vais)>
       AfterCloseCallback;
 
   // Construct a target for audio loopback which mixes multiple data streams
-  // into a single stream having the given |params|.
+  // into a single stream having the given |params|.  |worker_loop| is the loop
+  // on which AudioInputCallback methods are called and may or may not be the
+  // single thread that invokes the AudioInputStream methods.
   VirtualAudioInputStream(
       const AudioParameters& params,
-      const scoped_refptr<base::MessageLoopProxy>& message_loop,
+      const scoped_refptr<base::MessageLoopProxy>& worker_loop,
       const AfterCloseCallback& after_close_cb);
 
   virtual ~VirtualAudioInputStream();
 
   // AudioInputStream:
   virtual bool Open() OVERRIDE;
   virtual void Start(AudioInputCallback* callback) OVERRIDE;
   virtual void Stop() OVERRIDE;
   virtual void Close() OVERRIDE;
   virtual double GetMaxVolume() OVERRIDE;
@@ skipping 11 matching lines @@
 
   // Detaches a VirtualAudioOutputStream and removes it as input.
   virtual void RemoveOutputStream(VirtualAudioOutputStream* stream,
                                   const AudioParameters& output_params);
 
  private:
   friend class VirtualAudioInputStreamTest;
 
   typedef std::map<AudioParameters, LoopbackAudioConverter*> AudioConvertersMap;
 
-  // When Start() is called on this class, we continuously schedule this
-  // callback to render audio using any attached VirtualAudioOutputStreams until
-  // Stop() is called.
-  void ReadAudio(AudioBus* audio_bus);
+  // Pulls audio data from all attached VirtualAudioOutputStreams, mixes and
+  // converts the streams into one, and pushes the result to |callback_|.
+  // Invoked on the worker thread.
+  void PumpAudio(AudioBus* audio_bus);
 
-  const scoped_refptr<base::MessageLoopProxy> message_loop_;
+  const scoped_refptr<base::MessageLoopProxy> worker_loop_;
 
   AfterCloseCallback after_close_cb_;
 
   AudioInputCallback* callback_;
 
   // Non-const for testing.
   scoped_ptr<uint8[]> buffer_;
   AudioParameters params_;
 
+  // Guards concurrent access to the converter network: converters_, mixer_, and
+  // num_attached_output_streams_.
+  base::Lock converter_network_lock_;
+
   // AudioConverters associated with the attached VirtualAudioOutputStreams,
   // partitioned by common AudioParameters.
   AudioConvertersMap converters_;
 
   // AudioConverter that takes all the audio converters and mixes them into one
   // final audio stream.
   AudioConverter mixer_;
 
   // Number of currently attached VirtualAudioOutputStreams.
   int num_attached_output_streams_;
 
   // Handles callback timing for consumption of audio data.
   FakeAudioConsumer fake_consumer_;
 
+  base::ThreadChecker thread_checker_;
+
   DISALLOW_COPY_AND_ASSIGN(VirtualAudioInputStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_INPUT_STREAM_H_