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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // AudioOutputDispatcher is a single-threaded base class that dispatches
      6 // creation and deletion of audio output streams. AudioOutputProxy objects use
      7 // this class to allocate and recycle actual audio output streams. When playback
      8 // is started, the proxy calls StartStream() to get an output stream that it
      9 // uses to play audio. When playback is stopped, the proxy returns the stream
     10 // back to the dispatcher by calling StopStream().
     11 //
     12 // AudioManagerBase creates one specialization of AudioOutputDispatcher on the
     13 // audio thread for each possible set of audio parameters. I.e streams with
     14 // different parameters are managed independently.  The AudioOutputDispatcher
     15 // instance is then deleted on the audio thread when the AudioManager shuts
     16 // down.
     17 
     18 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
     19 #define MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
     20 
     21 #include "base/basictypes.h"
     22 #include "base/memory/ref_counted.h"
     23 #include "base/timer/timer.h"
     24 #include "media/audio/audio_io.h"
     25 #include "media/audio/audio_manager.h"
     26 #include "media/audio/audio_parameters.h"
     27 
     28 namespace base {
     29 class SingleThreadTaskRunner;
     30 }
     31 
     32 namespace media {
     33 
     34 class AudioOutputProxy;
     35 
     36 class MEDIA_EXPORT AudioOutputDispatcher
     37     : public base::RefCountedThreadSafe<AudioOutputDispatcher> {
     38  public:
     39   AudioOutputDispatcher(AudioManager* audio_manager,
     40                         const AudioParameters& params,
     41                         const std::string& device_id);
     42 
     43   // Called by AudioOutputProxy to open the stream.
     44   // Returns false, if it fails to open it.
     45   virtual bool OpenStream() = 0;
     46 
     47   // Called by AudioOutputProxy when the stream is started.
     48   // Uses |callback| to get source data and report errors, if any.
     49   // Does *not* take ownership of this callback.
     50   // Returns true if started successfully, false otherwise.
     51   virtual bool StartStream(AudioOutputStream::AudioSourceCallback* callback,
     52                            AudioOutputProxy* stream_proxy) = 0;
     53 
     54   // Called by AudioOutputProxy when the stream is stopped.
     55   // Ownership of the |stream_proxy| is passed to the dispatcher.
     56   virtual void StopStream(AudioOutputProxy* stream_proxy) = 0;
     57 
     58   // Called by AudioOutputProxy when the volume is set.
     59   virtual void StreamVolumeSet(AudioOutputProxy* stream_proxy,
     60                                double volume) = 0;
     61 
     62   // Called by AudioOutputProxy when the stream is closed.
     63   virtual void CloseStream(AudioOutputProxy* stream_proxy) = 0;
     64 
     65   // Called on the audio thread when the AudioManager is shutting down.
     66   virtual void Shutdown() = 0;
     67 
     68   const std::string& device_id() const { return device_id_; }
     69 
     70  protected:
     71   friend class base::RefCountedThreadSafe<AudioOutputDispatcher>;
     72   virtual ~AudioOutputDispatcher();
     73 
     74   // A no-reference-held pointer (we don't want circular references) back to the
     75   // AudioManager that owns this object.
     76   AudioManager* audio_manager_;
     77   const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
     78   const AudioParameters params_;
     79   std::string device_id_;
     80 
     81  private:
     82   DISALLOW_COPY_AND_ASSIGN(AudioOutputDispatcher);
     83 };
     84 
     85 }  // namespace media
     86 
     87 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
     88