Remove "high"-latency audio code path

media/audio/audio_output_controller.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_AUDIO_OUTPUT_CONTROLLER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/synchronization/lock.h"
 #include "base/time.h"
 #include "media/audio/audio_buffers_state.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/simple_sources.h"
 
 namespace base {
 class WaitableEvent;
 }  // namespace base
 
 class MessageLoop;
 
 // An AudioOutputController controls an AudioOutputStream and provides data
 // to this output stream. It has an important function that it executes
 // audio operations like play, pause, stop, etc. on a separate thread,
 // namely the audio controller thread.

[henrika (OOO until Aug 14), 2012/01/29 20:54:00]

Can we please change this comment as well while we are doing work in this area.
I've always found it confusing that we say "audio-controller thread" when it is
fact the audio-manager thread. Talking about an audio-controller thread makes it
sound as is one thread is created per controller and this is not the case.

[vrk (LEFT CHROMIUM), 2012/01/31 23:53:08]

Sure! Done, and combed through the comments in this file to specify audio
manager thread.
Yeah, especially since the comment above Create() basically said that, too :)
Fixed the Create() comment as well.

 //
 // All the public methods of AudioOutputController are non-blocking.
 // The actual operations are performed on the audio thread.
 //
-// Here is a state diagram for the AudioOutputController for default low
-// latency mode; in normal latency mode there is no "starting" or "paused when
-// starting" states, "created" immediately switches to "playing":
+// Here is a state diagram for the AudioOutputController:
 //
 //             .----------------------->  [ Closed / Error ]  <------.
 //             |                                   ^                 |
 //             |                                   |                 |
 //        [ Created ]  -->  [ Starting ]  -->  [ Playing ]  -->  [ Paused ]
 //             ^                 |                 ^                |  ^
 //             |                 |                 |                |  |
 //             |                 |                 `----------------'  |
 //             |                 V                                     |
 //             |        [ PausedWhenStarting ] ------------------------'
 //             |
 //       *[  Empty  ]
 //
 // * Initial state
 //
-// There are two modes of buffering operations supported by this class.
-//
-// Regular latency mode:
-//   In this mode we receive signals from AudioOutputController and then we
-//   enqueue data into it.
-//
-// Low latency mode:
-//   In this mode a DataSource object is given to the AudioOutputController
-//   and AudioOutputController reads from it synchronously.
+// The AudioOutputStream can request data from the AudioOutputController via the
+// AudioSourceCallback interface. AudioOutputController uses the SyncReader

[henrika (OOO until Aug 14), 2012/01/29 20:54:00]

I think we call the same interface on the render side AudioSink and not Source.
Might be a bit confusing. I feel that Sink is the the correct term since the
interface specifies a data consumption. 

[vrk (LEFT CHROMIUM), 2012/01/31 23:53:08]

Yeah, I am planning to go through and rename some of these interfaces and
methods to make things more uniform. Probably in a follow-up CL?

For now, I'll leave this comment as-is if that's okay.

[henrika (OOO until Aug 14), 2012/02/01 13:11:29]

Sounds fine.

+// passed to it via construction to synchronously fulfill this read request.
 //
 // The audio thread itself is owned by the AudioManager that the
 // AudioOutputController holds a reference to.  When performing tasks on the
 // audio thread, the controller must not add or release references to the
 // AudioManager or itself (since it in turn holds a reference to the manager),
 // for delayed tasks as it can slow down or even prevent normal shut down.
 // So, for tasks on the audio thread, the controller uses WeakPtr which enables
 // us to safely cancel pending polling tasks.
 // The owner of the audio thread, AudioManager, will take care of properly
 // shutting it down.
@@ skipping 12 matching lines @@
 
   // An event handler that receives events from the AudioOutputController. The
   // following methods are called on the audio controller thread.
   class MEDIA_EXPORT EventHandler {
    public:
     virtual ~EventHandler() {}
     virtual void OnCreated(AudioOutputController* controller) = 0;
     virtual void OnPlaying(AudioOutputController* controller) = 0;
     virtual void OnPaused(AudioOutputController* controller) = 0;
     virtual void OnError(AudioOutputController* controller, int error_code) = 0;
-
-    // Audio controller asks for more data.
-    // |pending_bytes| is the number of bytes still on the controller.
-    // |timestamp| is then time when |pending_bytes| is recorded.
-    virtual void OnMoreData(AudioOutputController* controller,
-                            AudioBuffersState buffers_state) = 0;
   };
 
   // A synchronous reader interface used by AudioOutputController for
   // synchronous reading.
   class SyncReader {
    public:
     virtual ~SyncReader() {}
 
     // Notify the synchronous reader the number of bytes in the
     // AudioOutputController not yet played. This is used by SyncReader to
@@ skipping 16 matching lines @@
   };
 
   // Factory method for creating an AudioOutputController.
   // If successful, an audio controller thread is created. The audio device
   // will be created on the audio controller thread and when that is done
   // event handler will receive a OnCreated() call.
   static scoped_refptr<AudioOutputController> Create(
       AudioManager* audio_manager,
       EventHandler* event_handler,
       const AudioParameters& params,
-      // Soft limit for buffer capacity in this controller. This parameter
-      // is used only in regular latency mode.
-      uint32 buffer_capacity);
-
-  // Factory method for creating a low latency audio stream.
-  static scoped_refptr<AudioOutputController> CreateLowLatency(
-      AudioManager* audio_manager,
-      EventHandler* event_handler,
-      const AudioParameters& params,
       // External synchronous reader for audio controller.
       SyncReader* sync_reader);
 
   // Methods to control playback of the stream.
 
   // Starts the playback of this audio output stream.
   void Play();
 
   // Pause this audio output stream.
   void Pause();
 
   // Discard all audio data buffered in this output stream. This method only
   // has effect when the stream is paused.
   void Flush();
 
   // Closes the audio output stream. The state is changed and the resources
   // are freed on the audio thread. closed_task is executed after that.
   // Callbacks (EventHandler and SyncReader) must exist until closed_task is
   // called.
   //
   // It is safe to call this method more than once. Calls after the first one
   // will have no effect.
   void Close(const base::Closure& closed_task);
 
   // Sets the volume of the audio output stream.
   void SetVolume(double volume);
 
-  // Enqueue audio |data| into the controller. This method is used only in
-  // the regular latency mode and it is illegal to call this method when
-  // SyncReader is present.
-  void EnqueueData(const uint8* data, uint32 size);
-
-  bool LowLatencyMode() const { return sync_reader_ != NULL; }
-
   ///////////////////////////////////////////////////////////////////////////
   // AudioSourceCallback methods.
   virtual uint32 OnMoreData(AudioOutputStream* stream,
                             uint8* dest,
                             uint32 max_size,
                             AudioBuffersState buffers_state) OVERRIDE;
   virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
   virtual void WaitTillDataReady() OVERRIDE;
 
  protected:
@@ skipping 12 matching lines @@
   friend class base::RefCountedThreadSafe<AudioOutputController>;
   virtual ~AudioOutputController();
 
  private:
   // We are polling sync reader if data became available.
   static const int kPollNumAttempts;
   static const int kPollPauseInMilliseconds;
 
   AudioOutputController(AudioManager* audio_manager,
                         EventHandler* handler,
-                        uint32 capacity, SyncReader* sync_reader);
+                        SyncReader* sync_reader);
 
   // The following methods are executed on the audio controller thread.
   void DoCreate(const AudioParameters& params);
   void DoPlay();
   void PollAndStartIfDataReady();
   void DoPause();
   void DoFlush();
   void DoClose(const base::Closure& closed_task);
   void DoSetVolume(double volume);
   void DoReportError(int code);
 
-  // Helper method to submit a OnMoreData() call to the event handler.
-  void SubmitOnMoreData_Locked();
-
   // Helper method that starts physical stream.
   void StartStream();
 
   // Helper method that stops, closes, and NULLs |*stream_|.
   // Signals event when done if it is not NULL.
   void DoStopCloseAndClearStream(base::WaitableEvent *done);
 
   scoped_refptr<AudioManager> audio_manager_;
   // |handler_| may be called only if |state_| is not kClosed.
   EventHandler* handler_;
   AudioOutputStream* stream_;
 
   // The current volume of the audio stream.
   double volume_;
 
   // |state_| is written on the audio controller thread and is read on the
   // hardware audio thread. These operations need to be locked. But lock
   // is not required for reading on the audio controller thread.
   State state_;
 
-  AudioBuffersState buffers_state_;
-
-  // The |lock_| must be acquired whenever we access |buffer_|.
+  // The |lock_| must be acquired whenever we access |state_| from a thread
+  // other than the audio controller thread.

[henrika (OOO until Aug 14), 2012/01/29 20:54:00]

Rename to audio-manager thread?

[vrk (LEFT CHROMIUM), 2012/01/31 23:53:08]

Done.

   base::Lock lock_;
 
-  media::SeekableBuffer buffer_;
-
-  bool pending_request_;
-
   // SyncReader is used only in low latency mode for synchronous reading.
   SyncReader* sync_reader_;
 
   // The message loop of audio thread that this object runs on.
   scoped_refptr<base::MessageLoopProxy> message_loop_;
 
   // When starting stream we wait for data to become available.
   // Number of times left.
   int number_polling_attempts_left_;
 
   // Used to post delayed tasks to ourselves that we can cancel.
   // We don't want the tasks to hold onto a reference as it will slow down
   // shutdown and force it to wait for the most delayed task.
   // Also, if we're shutting down, we do not want to poll for more data.
   base::WeakPtrFactory<AudioOutputController> weak_this_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_