Audio software mixer.

media/audio/audio_output_dispatcher.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.
 
-// AudioOutputDispatcher is a single-threaded class that dispatches creation and
-// deletion of audio output streams. AudioOutputProxy objects use this class to
-// allocate and recycle actual audio output streams. When playback is started,
-// the proxy calls StreamStarted() to get an output stream that it uses to play
-// audio. When playback is stopped, the proxy returns the stream back to the
-// dispatcher by calling StreamStopped().
+// AudioOutputDispatcher is a single-threaded base class that dispatches
+// creation and deletion of audio output streams. AudioOutputProxy objects use
+// this class to allocate and recycle actual audio output streams. When playback
+// is started, the proxy calls StreamStarted() to get an output stream that it
+// uses to play audio. When playback is stopped, the proxy returns the stream
+// back to the dispatcher by calling StreamStopped().
 //
-// To avoid opening and closing audio devices more frequently than necessary,
-// each dispatcher has a pool of inactive physical streams. A stream is closed
-// only if it hasn't been used for a certain period of time (specified via the
-// constructor).
-//
-// AudioManagerBase creates one AudioOutputDispatcher on the audio thread for
-// each possible set of audio parameters. I.e streams with different parameters
-// are managed independently.  The AudioOutputDispatcher instance is then
-// deleted on the audio thread when the AudioManager shuts down.
+// AudioManagerBase creates one specialization of AudioOutputDispatcher on the
+// audio thread for each possible set of audio parameters. I.e streams with
+// different parameters are managed independently.  The AudioOutputDispatcher
+// instance is then deleted on the audio thread when the AudioManager shuts
+// down.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_
 
 #include <vector>
 #include <list>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
-#include "base/memory/weak_ptr.h"
 #include "base/timer.h"
+#include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/audio_parameters.h"
 
-class AudioOutputStream;
+class AudioOutputProxy;
 class MessageLoop;
 
 class MEDIA_EXPORT AudioOutputDispatcher
     : public base::RefCountedThreadSafe<AudioOutputDispatcher> {
  public:
-  // |close_delay_ms| specifies delay after the stream is paused until
-  // the audio device is closed.
   AudioOutputDispatcher(AudioManager* audio_manager,
-                        const AudioParameters& params,
-                        base::TimeDelta close_delay);
-  ~AudioOutputDispatcher();
+                        const AudioParameters& params);
 
-  // Called by AudioOutputProxy when the stream is closed. Opens a new
-  // physical stream if there are no pending streams in |idle_streams_|.
+  // Called by AudioOutputProxy when the stream is opened.
   // Returns false, if it fails to open it.
-  bool StreamOpened();
+  virtual bool StreamOpened() = 0;

[tommi (sloooow) - chröme, 2012/04/03 13:47:51]

Can you change this method name to OpenStream.  As is, the name+comments are
confusing.  Then update the comments to something like:

// Called by AudioOutputProxy when the stream needs to be opened.
virtual bool OpenStream() = 0;

[enal1, 2012/04/04 18:46:55]

Done.

 
-  // Called by AudioOutputProxy when the stream is started. If there
-  // are pending streams in |idle_streams_| then it returns one of them,
-  // otherwise creates a new one. Returns a physical stream that must
-  // be used, or NULL if it fails to open audio device. Ownership of
-  // the result is passed to the caller.
-  AudioOutputStream* StreamStarted();
+  // Called by AudioOutputProxy when the stream is started.
+  // Ownership of the result is passed to the caller.
+  virtual AudioOutputStream* StreamStarted(
+      AudioOutputStream::AudioSourceCallback* callback,

[tommi (sloooow) - chröme, 2012/04/03 13:47:51]

add documentation for the new parameters

[enal1, 2012/04/04 18:46:55]

Done.

+      AudioOutputProxy* stream_proxy) = 0;
 
-  // Called by AudioOutputProxy when the stream is stopped.  Holds the
-  // stream temporarily in |pausing_streams_| and then |stream| is
-  // added to the pool of pending streams (i.e. |idle_streams_|).
+  // Called by AudioOutputProxy when the stream is stopped.
   // Ownership of the |stream| is passed to the dispatcher.
-  void StreamStopped(AudioOutputStream* stream);
+  virtual void StreamStopped(AudioOutputStream* physical_stream,

[tommi (sloooow) - chröme, 2012/04/03 13:47:51]

documentation for the parameters

[enal1, 2012/04/04 18:46:55]

Done.

+                             AudioOutputProxy* stream_proxy) = 0;
+
+
+  // Called by AudioOutputProxy when the volume is set.
+  virtual void StreamVolumeSet(AudioOutputStream* physical_stream,
+                               double volume) = 0;
 
   // Called by AudioOutputProxy when the stream is closed.
-  void StreamClosed();
+  virtual void StreamClosed(AudioOutputProxy* stream_proxy) = 0;
 
   // Called on the audio thread when the AudioManager is shutting down.
-  void Shutdown();
+  virtual void Shutdown() = 0;
 
- private:
-  friend class AudioOutputProxyTest;
-
-  // Creates a new physical output stream, opens it and pushes to
-  // |idle_streams_|.  Returns false if the stream couldn't be created or
-  // opened.
-  bool CreateAndOpenStream();
-
-  // A task scheduled by StreamStarted(). Opens a new stream and puts
-  // it in |idle_streams_|.
-  void OpenTask();
-
-  // Before a stream is reused, it should sit idle for a bit.  This task is
-  // called once that time has elapsed.
-  void StopStreamTask();
-
-  // Called by |close_timer_|. Closes all pending stream.
-  void ClosePendingStreams();
+ protected:
+  friend class base::RefCountedThreadSafe<AudioOutputDispatcher>;
+  ~AudioOutputDispatcher();
 
   // A no-reference-held pointer (we don't want circular references) back to the
   // AudioManager that owns this object.
   AudioManager* audio_manager_;
   MessageLoop* message_loop_;
   AudioParameters params_;
 
-  base::TimeDelta pause_delay_;
-  size_t paused_proxies_;
-  typedef std::list<AudioOutputStream*> AudioOutputStreamList;
-  AudioOutputStreamList idle_streams_;
-  AudioOutputStreamList pausing_streams_;
-
-  // Used to post delayed tasks to ourselves that we cancel inside Shutdown().
-  base::WeakPtrFactory<AudioOutputDispatcher> weak_this_;
-  base::DelayTimer<AudioOutputDispatcher> close_timer_;
-
+ private:
   DISALLOW_COPY_AND_ASSIGN(AudioOutputDispatcher);
 };
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_H_