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/atomic_ref_count.h"
#include "base/callback.h"
#include "base/memory/ref_counted.h"
#include "base/timer/timer.h"
#include "build/build_config.h"
#include "media/audio/audio_io.h"
#include "media/audio/audio_manager.h"
#include "media/audio/audio_power_monitor.h"
#include "media/audio/audio_source_diverter.h"
#include "media/audio/simple_sources.h"
#include "media/base/media_export.h"

// 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 manager thread.
//
// All the public methods of AudioOutputController are non-blocking.
// The actual operations are performed on the audio manager thread.
//
// Here is a state transition diagram for the AudioOutputController:
//
//   *[ Empty ]  -->  [ Created ]  -->  [ Playing ]  -------.
//        |                |               |    ^           |
//        |                |               |    |           |
//        |                |               |    |           v
//        |                |               |    `-----  [ Paused ]
//        |                |               |                |
//        |                v               v                |
//        `----------->  [      Closed       ]  <-----------'
//
// * Initial state
//
// At any time after reaching the Created state but before Closed, the
// AudioOutputController may be notified of a device change via
// OnDeviceChange().  As the OnDeviceChange() is processed, state transitions
// will occur, ultimately ending up in an equivalent pre-call state.  E.g., if
// the state was Paused, the new state will be Created, since these states are
// all functionally equivalent and require a Play() call to continue to the next
// state.
//
// The AudioOutputStream can request data from the AudioOutputController via the
// AudioSourceCallback interface. AudioOutputController uses the SyncReader
// passed to it via construction to synchronously fulfill this read request.
//

namespace media {

class MEDIA_EXPORT AudioOutputController
    : public base::RefCountedThreadSafe<AudioOutputController>,
      public AudioOutputStream::AudioSourceCallback,
      public AudioSourceDiverter,
      NON_EXPORTED_BASE(public AudioManager::AudioDeviceListener)  {
 public:
  // An event handler that receives events from the AudioOutputController. The
  // following methods are called on the audio manager thread.
  class MEDIA_EXPORT EventHandler {
   public:
    virtual void OnCreated() = 0;
    virtual void OnPlaying() = 0;
    virtual void OnPaused() = 0;
    virtual void OnError() = 0;

   protected:
    virtual ~EventHandler() {}
  };

  // A synchronous reader interface used by AudioOutputController for
  // synchronous reading.
  // TODO(crogers): find a better name for this class and the Read() method
  // now that it can handle synchronized I/O.
  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
    // prepare more data and perform synchronization.
    virtual void UpdatePendingBytes(uint32 bytes) = 0;

    // Attempts to completely fill |dest|, zeroing |dest| if the request can not
    // be fulfilled (due to timeout).
    virtual void Read(AudioBus* dest) = 0;

    // Close this synchronous reader.
    virtual void Close() = 0;
  };

  // Factory method for creating an AudioOutputController.
  // This also creates and opens an AudioOutputStream on the audio manager
  // thread, and if this is successful, the |event_handler| will receive an
  // OnCreated() call from the same audio manager thread.  |audio_manager| must
  // outlive AudioOutputController.
  // The |output_device_id| can be either empty (default device) or specify a
  // specific hardware device for audio output.
  static scoped_refptr<AudioOutputController> Create(
      AudioManager* audio_manager, EventHandler* event_handler,
      const AudioParameters& params, const std::string& output_device_id,
      SyncReader* sync_reader);

  // Indicates whether audio power level analysis will be performed.  If false,
  // ReadCurrentPowerAndClip() can not be called.
  static bool will_monitor_audio_levels() {
#if defined(OS_ANDROID) || defined(OS_IOS)
    return false;
#else
    return true;
#endif
  }

  // Methods to control playback of the stream.

  // Starts the playback of this audio output stream.
  void Play();

  // Pause this audio output stream.
  void Pause();

  // Closes the audio output stream. The state is changed and the resources
  // are freed on the audio manager 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);

  // Calls |callback| (on the caller's thread) with the current output
  // device ID.
  void GetOutputDeviceId(
      base::Callback<void(const std::string&)> callback) const;

  // Changes which output device to use. If desired, you can provide a
  // callback that will be notified (on the thread you called from)
  // when the function has completed execution.
  //
  // Changing the output device causes the controller to go through
  // the same state transition back to the current state as a call to
  // OnDeviceChange (unless it is currently diverting, see
  // Start/StopDiverting below, in which case the state transition
  // will happen when StopDiverting is called).
  void SwitchOutputDevice(const std::string& output_device_id,
                          const base::Closure& callback);

  // AudioSourceCallback implementation.
  int OnMoreData(AudioBus* dest, uint32 total_bytes_delay) override;
  void OnError(AudioOutputStream* stream) override;

  // AudioDeviceListener implementation.  When called AudioOutputController will
  // shutdown the existing |stream_|, transition to the kRecreating state,
  // create a new stream, and then transition back to an equivalent state prior
  // to being called.
  void OnDeviceChange() override;

  // AudioSourceDiverter implementation.
  const AudioParameters& GetAudioParameters() override;
  void StartDiverting(AudioOutputStream* to_stream) override;
  void StopDiverting() override;

  // Accessor for AudioPowerMonitor::ReadCurrentPowerAndClip().  See comments in
  // audio_power_monitor.h for usage.  This may be called on any thread.
  std::pair<float, bool> ReadCurrentPowerAndClip();

 protected:
  // Internal state of the source.
  enum State {
    kEmpty,
    kCreated,
    kPlaying,
    kPaused,
    kClosed,
    kError,
  };

  // Time constant for AudioPowerMonitor.  See AudioPowerMonitor ctor comments
  // for semantics.  This value was arbitrarily chosen, but seems to work well.
  enum { kPowerMeasurementTimeConstantMillis = 10 };

  friend class base::RefCountedThreadSafe<AudioOutputController>;
  ~AudioOutputController() override;

 private:
  AudioOutputController(AudioManager* audio_manager, EventHandler* handler,
                        const AudioParameters& params,
                        const std::string& output_device_id,
                        SyncReader* sync_reader);

  // The following methods are executed on the audio manager thread.
  void DoCreate(bool is_for_device_change);
  void DoPlay();
  void DoPause();
  void DoClose();
  void DoSetVolume(double volume);
  std::string DoGetOutputDeviceId() const;
  void DoSwitchOutputDevice(const std::string& output_device_id);
  void DoReportError();
  void DoStartDiverting(AudioOutputStream* to_stream);
  void DoStopDiverting();

  // Helper method that stops the physical stream.
  void StopStream();

  // Helper method that stops, closes, and NULLs |*stream_|.
  void DoStopCloseAndClearStream();

  // Checks if a stream was started successfully but never calls OnMoreData().
  void WedgeCheck();

  AudioManager* const audio_manager_;
  const AudioParameters params_;
  EventHandler* const handler_;

  // Specifies the device id of the output device to open or empty for the
  // default output device.
  std::string output_device_id_;

  AudioOutputStream* stream_;

  // When non-NULL, audio is being diverted to this stream.
  AudioOutputStream* diverting_to_stream_;

  // The current volume of the audio stream.
  double volume_;

  // |state_| may only be used on the audio manager thread.
  State state_;

  // SyncReader is used only in low latency mode for synchronous reading.
  SyncReader* const sync_reader_;

  // The message loop of audio manager thread that this object runs on.
  const scoped_refptr<base::SingleThreadTaskRunner> message_loop_;

  // Scans audio samples from OnMoreData() as input to compute power levels.
  AudioPowerMonitor power_monitor_;

  // Flags when we've asked for a stream to start but it never did.
  base::AtomicRefCount on_more_io_data_called_;
  scoped_ptr<base::OneShotTimer> wedge_timer_;

  // Flag which indicates errors received during Stop/Close should be ignored.
  // These errors are generally harmless since a fresh stream is about to be
  // recreated, but if forwarded, renderer side clients may consider them
  // catastrophic and abort their operations.
  //
  // If |stream_| is started then |ignore_errors_during_stop_close_| must only
  // be accessed while |error_lock_| is held.
  bool ignore_errors_during_stop_close_;
  base::Lock error_lock_;

  DISALLOW_COPY_AND_ASSIGN(AudioOutputController);
};

}  // namespace media

#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_CONTROLLER_H_