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// 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.
// Audio rendering unit utilizing audio output stream provided by browser
// process through IPC.
// Relationship of classes.
// AudioOutputController AudioOutputDevice
// ^ ^
// | |
// v IPC v
// AudioRendererHost <---------> AudioOutputIPC (AudioMessageFilter)
// Transportation of audio samples from the render to the browser process
// is done by using shared memory in combination with a sync socket pair
// to generate a low latency transport. The AudioOutputDevice user registers an
// AudioOutputDevice::RenderCallback at construction and will be polled by the
// AudioOutputDevice for audio to be played out by the underlying audio layers.
// State sequences.
// Task [IO thread] IPC [IO thread]
// Start -> CreateStreamOnIOThread -----> CreateStream ------>
// <- OnStreamCreated <- AudioMsg_NotifyStreamCreated <-
// ---> PlayOnIOThread -----------> PlayStream -------->
// Optionally Play() / Pause() sequences may occur:
// Play -> PlayOnIOThread --------------> PlayStream --------->
// Pause -> PauseOnIOThread ------------> PauseStream -------->
// (note that Play() / Pause() sequences before OnStreamCreated are
// deferred until OnStreamCreated, with the last valid state being used)
// AudioOutputDevice::Render => audio transport on audio thread =>
// |
// Stop --> ShutDownOnIOThread --------> CloseStream -> Close
// This class utilizes several threads during its lifetime, namely:
// 1. Creating thread.
// Must be the main render thread.
// 2. Control thread (may be the main render thread or another thread).
// The methods: Start(), Stop(), Play(), Pause(), SetVolume()
// must be called on the same thread.
// 3. IO thread (internal implementation detail - not exposed to public API)
// The thread within which this class receives all the IPC messages and
// IPC communications can only happen in this thread.
// 4. Audio transport thread (See AudioDeviceThread).
// Responsible for calling the AudioThreadCallback implementation that in
// turn calls AudioRendererSink::RenderCallback which feeds audio samples to
// the audio layer in the browser process using sync sockets and shared
// memory.
// Implementation notes:
// - The user must call Stop() before deleting the class instance.
#include "base/basictypes.h"
#include "base/bind.h"
#include "base/memory/scoped_ptr.h"
#include "base/message_loop.h"
#include "base/shared_memory.h"
#include "media/base/media_export.h"
#include "media/audio/audio_device_thread.h"
#include "media/audio/audio_output_ipc.h"
#include "media/audio/audio_parameters.h"
#include "media/audio/scoped_loop_observer.h"
#include "media/base/audio_renderer_sink.h"
namespace media {
class MEDIA_EXPORT AudioOutputDevice
: NON_EXPORTED_BASE(public AudioRendererSink),
public AudioOutputIPCDelegate,
NON_EXPORTED_BASE(public ScopedLoopObserver) {
// AudioRendererSink implementation.
virtual void Initialize(const AudioParameters& params,
RenderCallback* callback) OVERRIDE;
virtual void InitializeIO(const AudioParameters& params,
int input_channels,
RenderCallback* callback) OVERRIDE;
virtual void Start() OVERRIDE;
virtual void Stop() OVERRIDE;
virtual void Play() OVERRIDE;
virtual void Pause(bool flush) OVERRIDE;
virtual bool SetVolume(double volume) OVERRIDE;
// Methods called on IO thread ----------------------------------------------
// AudioOutputIPCDelegate methods.
virtual void OnStateChanged(AudioOutputIPCDelegate::State state) OVERRIDE;
virtual void OnStreamCreated(base::SharedMemoryHandle handle,
base::SyncSocket::Handle socket_handle,
int length) OVERRIDE;
virtual void OnIPCClosed() OVERRIDE;
// Creates an uninitialized AudioOutputDevice. Clients must call Initialize()
// before using.
AudioOutputDevice(AudioOutputIPC* ipc,
const scoped_refptr<base::MessageLoopProxy>& io_loop);
// Magic required by ref_counted.h to avoid any code deleting the object
// accidentally while there are references to it.
friend class base::RefCountedThreadSafe<AudioOutputDevice>;
virtual ~AudioOutputDevice();
// Accessors for subclasses (via IO thread only).
int stream_id() const { return stream_id_; }
AudioOutputIPC* audio_output_ipc() const { return ipc_; }
// Note: The ordering of members in this enum is critical to correct behavior!
enum State {
IPC_CLOSED, // No more IPCs can take place.
IDLE, // Not started.
CREATING_STREAM, // Waiting for OnStreamCreated() to be called back.
PAUSED, // Paused. OnStreamCreated() has been called. Can Play()/Stop().
PLAYING, // Playing back. Can Pause()/Stop().
// Methods called on IO thread ----------------------------------------------
// The following methods are tasks posted on the IO thread that needs to
// be executed on that thread. They interact with AudioMessageFilter and
// sends IPC messages on that thread.
void CreateStreamOnIOThread(const AudioParameters& params,
int input_channels);
void PlayOnIOThread();
void PauseOnIOThread(bool flush);
void ShutDownOnIOThread();
void SetVolumeOnIOThread(double volume);
// MessageLoop::DestructionObserver implementation for the IO loop.
// If the IO loop dies before we do, we shut down the audio thread from here.
virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
AudioParameters audio_parameters_;
// The number of optional synchronized input channels having the same
// sample-rate and buffer-size as specified in audio_parameters_.
int input_channels_;
RenderCallback* callback_;
// A pointer to the IPC layer that takes care of sending requests over to
// the AudioRendererHost.
AudioOutputIPC* ipc_;
// Our stream ID on the message filter. Only accessed on the IO thread.
// Must only be modified on the IO thread.
int stream_id_;
// Current state (must only be accessed from the IO thread). See comments for
// State enum above.
State state_;
// State of Play() / Pause() calls before OnStreamCreated() is called.
bool play_on_start_;
// Our audio thread callback class. See source file for details.
class AudioThreadCallback;
// In order to avoid a race between OnStreamCreated and Stop(), we use this
// guard to control stopping and starting the audio thread.
base::Lock audio_thread_lock_;
AudioDeviceThread audio_thread_;
scoped_ptr<AudioOutputDevice::AudioThreadCallback> audio_callback_;
// Temporary hack to ignore OnStreamCreated() due to the user calling Stop()
// so we don't start the audio thread pointing to a potentially freed
// |callback_|.
// TODO(scherkus): Replace this by changing AudioRendererSink to either accept
// the callback via Start(). See for details.
bool stopping_hack_;
} // namespace media