author Oana Pop Rus <>
Thu, 11 Apr 2019 21:16:55 +0300
changeset 469046 e8de4ced5bb43d0ef7a481faf94d9d2bdcce584a
parent 468963 e725253ee97629bbed151cb7ba9c9ed0278f9921
child 469693 d47604394f78874f7eb109b49dec1f90ac9dc0f8
permissions -rw-r--r--
Backed out 6 changesets (bug 1531833) for geckoview failures on CLOSED TREE Backed out changeset f90ad6bb8ebd (bug 1531833) Backed out changeset 465570a54b46 (bug 1531833) Backed out changeset e725253ee976 (bug 1531833) Backed out changeset 74ad8e7a722b (bug 1531833) Backed out changeset b1268e5f7023 (bug 1531833) Backed out changeset e3ec78b2db1f (bug 1531833)

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at */


#include "nsAutoRef.h"
#include "AudioBufferUtils.h"
#include "AudioMixer.h"
#include "AudioSegment.h"
#include "SelfRef.h"
#include "mozilla/Atomics.h"
#include "mozilla/SharedThreadPool.h"
#include "mozilla/StaticPtr.h"

#include <thread>

#if defined(XP_WIN)
#  include "mozilla/audio/AudioNotificationReceiver.h"

struct cubeb_stream;

template <>
class nsAutoRefTraits<cubeb_stream> : public nsPointerRefTraits<cubeb_stream> {
  static void Release(cubeb_stream* aStream) { cubeb_stream_destroy(aStream); }

namespace mozilla {

 * Assume we can run an iteration of the MediaStreamGraph loop in this much time
 * or less.
 * We try to run the control loop at this rate.
static const int MEDIA_GRAPH_TARGET_PERIOD_MS = 10;

 * Assume that we might miss our scheduled wakeup of the MediaStreamGraph by
 * this much.
static const int SCHEDULE_SAFETY_MARGIN_MS = 10;

 * Try have this much audio buffered in streams and queued to the hardware.
 * The maximum delay to the end of the next control loop
 * There is no point in buffering more audio than this in a stream at any
 * given time (until we add processing).
 * This is not optimal yet.
static const int AUDIO_TARGET_MS =

class MediaStream;
class MediaStreamGraphImpl;

class AudioCallbackDriver;
class OfflineClockDriver;
class SystemClockDriver;

namespace dom {
enum class AudioContextOperation;

 * A driver is responsible for the scheduling of the processing, the thread
 * management, and give the different clocks to a MediaStreamGraph. This is an
 * abstract base class. A MediaStreamGraph can be driven by an
 * OfflineClockDriver, if the graph is offline, or a SystemClockDriver, if the
 * graph is real time.
 * A MediaStreamGraph holds an owning reference to its driver.
 * The lifetime of drivers is a complicated affair. Here are the different
 * scenarii that can happen:
 * Starting a MediaStreamGraph with an AudioCallbackDriver
 * - A new thread T is created, from the main thread.
 * - On this thread T, cubeb is initialized if needed, and a cubeb_stream is
 *   created and started
 * - The thread T posts a message to the main thread to terminate itself.
 * - The graph runs off the audio thread
 * Starting a MediaStreamGraph with a SystemClockDriver:
 * - A new thread T is created from the main thread.
 * - The graph runs off this thread.
 * Switching from a SystemClockDriver to an AudioCallbackDriver:
 * - A new AudioCallabackDriver is created and initialized on the graph thread
 * - At the end of the MSG iteration, the SystemClockDriver transfers its timing
 *   info and a reference to itself to the AudioCallbackDriver. It then starts
 *   the AudioCallbackDriver.
 * - When the AudioCallbackDriver starts, it checks if it has been switched from
 *   a SystemClockDriver, and if that is the case, sends a message to the main
 *   thread to shut the SystemClockDriver thread down.
 * - The graph now runs off an audio callback
 * Switching from an AudioCallbackDriver to a SystemClockDriver:
 * - A new SystemClockDriver is created, and set as mNextDriver.
 * - At the end of the MSG iteration, the AudioCallbackDriver transfers its
 *   timing info and a reference to itself to the SystemClockDriver. A new
 *   SystemClockDriver is started from the current audio thread.
 * - When starting, the SystemClockDriver checks if it has been switched from an
 *   AudioCallbackDriver. If yes, it creates a new temporary thread to release
 *   the cubeb_streams. This temporary thread closes the cubeb_stream, and
 *   then dispatches a message to the main thread to be terminated.
 * - The graph now runs off a normal thread.
 * Two drivers cannot run at the same time for the same graph. The thread safety
 * of the different attributes of drivers, and they access pattern is documented
 * next to the members themselves.
class GraphDriver {
  explicit GraphDriver(MediaStreamGraphImpl* aGraphImpl);

  /* For {System,Offline}ClockDriver, this waits until it's time to process
   * more data.  For AudioCallbackDriver, this is a no-op. */
  virtual void WaitForNextIteration() = 0;
  /* Wakes up the graph if it is waiting. */
  virtual void WakeUp() = 0;
  /* Start the graph, init the driver, start the thread.
   * A driver cannot be started twice, it must be shutdown
   * before being started again. */
  virtual void Start() = 0;
  /* Revive this driver, as more messages just arrived. */
  virtual void Revive() = 0;
  /* Shutdown GraphDriver (synchronously) */
  virtual void Shutdown() = 0;
  /* Rate at which the GraphDriver runs, in ms. This can either be user
   * controlled (because we are using a {System,Offline}ClockDriver, and decide
   * how often we want to wakeup/how much we want to process per iteration), or
   * it can be indirectly set by the latency of the audio backend, and the
   * number of buffers of this audio backend: say we have four buffers, and 40ms
   * latency, we will get a callback approximately every 10ms. */
  virtual uint32_t IterationDuration() = 0;

  /* Return whether we are switching or not. */
  bool Switching();
  /* Implement the switching of the driver and the necessary updates */
  void SwitchToNextDriver();

  // Those are simply or setting the associated pointer, but assert that the
  // lock is held.
  GraphDriver* NextDriver();
  GraphDriver* PreviousDriver();
  void SetPreviousDriver(GraphDriver* aPreviousDriver);

  GraphTime IterationEnd() { return mIterationEnd; }

  virtual AudioCallbackDriver* AsAudioCallbackDriver() { return nullptr; }

  virtual OfflineClockDriver* AsOfflineClockDriver() { return nullptr; }

  virtual SystemClockDriver* AsSystemClockDriver() { return nullptr; }

   * Tell the driver it has to stop and return the current time of the graph, so
   * another driver can start from the right point in time.
  virtual void SwitchAtNextIteration(GraphDriver* aDriver);

   * Set the time for a graph, on a driver. This is used so a new driver just
   * created can start at the right point in time.
  void SetGraphTime(GraphDriver* aPreviousDriver,
                    GraphTime aLastSwitchNextIterationStart,
                    GraphTime aLastSwitchNextIterationEnd);
   * Call this to indicate that another iteration of the control loop is
   * required on its regular schedule. The monitor must not be held.
   * This function has to be idempotent.
  void EnsureNextIteration();

  MediaStreamGraphImpl* GraphImpl() const { return mGraphImpl; }

#ifdef DEBUG
  // True if the current thread is driving the MSG.
  bool OnGraphThread();
  // True if the current thread is the GraphDriver's thread.
  virtual bool OnThread() = 0;
  // GraphDriver's thread has started and the thread is running.
  virtual bool ThreadRunning() = 0;

  GraphTime StateComputedTime() const;
  // Sets the associated pointer, asserting that the lock is held
  void SetNextDriver(GraphDriver* aNextDriver);

  // Time of the start of this graph iteration. This must be accessed while
  // having the monitor.
  GraphTime mIterationStart;
  // Time of the end of this graph iteration. This must be accessed while having
  // the monitor.
  GraphTime mIterationEnd;
  // The MediaStreamGraphImpl associated with this driver.
  const RefPtr<MediaStreamGraphImpl> mGraphImpl;

  // This is non-null only when this driver has recently switched from an other
  // driver, and has not cleaned it up yet (for example because the audio stream
  // is currently calling the callback during initialization).
  // This is written to when changing driver, from the previous driver's thread,
  // or a thread created for the occasion. This is read each time we need to
  // check whether we're changing driver (in Switching()), from the graph
  // thread.
  // This must be accessed using the {Set,Get}PreviousDriver methods.
  RefPtr<GraphDriver> mPreviousDriver;
  // This is non-null only when this driver is going to switch to an other
  // driver at the end of this iteration.
  // This must be accessed using the {Set,Get}NextDriver methods.
  RefPtr<GraphDriver> mNextDriver;
  virtual ~GraphDriver() {}

class MediaStreamGraphInitThreadRunnable;

 * This class is a driver that manages its own thread.
class ThreadedDriver : public GraphDriver {
  explicit ThreadedDriver(MediaStreamGraphImpl* aGraphImpl);
  virtual ~ThreadedDriver();
  void WaitForNextIteration() override;
  void WakeUp() override;
  void Start() override;
  void Revive() override;
  void Shutdown() override;
   * Runs main control loop on the graph thread. Normally a single invocation
   * of this runs for the entire lifetime of the graph thread.
  void RunThread();
  friend class MediaStreamGraphInitThreadRunnable;
  uint32_t IterationDuration() override { return MEDIA_GRAPH_TARGET_PERIOD_MS; }

  nsIThread* Thread() { return mThread; }

  bool OnThread() override {
    return !mThread || mThread->EventTarget()->IsOnCurrentThread();

  bool ThreadRunning() override { return mThreadRunning; }
   * Return the TimeDuration to wait before the next rendering iteration.
  virtual TimeDuration WaitInterval() = 0;
  /* When the graph wakes up to do an iteration, implementations return the
   * range of time that will be processed.  This is called only once per
   * iteration; it may determine the interval from state in a previous
   * call. */
  virtual MediaTime GetIntervalForIteration() = 0;

  nsCOMPtr<nsIThread> mThread;

  // This is true if the thread is running. It is false
  // before starting the thread and after stopping it.
  Atomic<bool> mThreadRunning;

 * A SystemClockDriver drives a MediaStreamGraph using a system clock, and waits
 * using a monitor, between each iteration.
class SystemClockDriver : public ThreadedDriver {
  explicit SystemClockDriver(MediaStreamGraphImpl* aGraphImpl);
  virtual ~SystemClockDriver();
  TimeDuration WaitInterval() override;
  MediaTime GetIntervalForIteration() override;
  void MarkAsFallback();
  bool IsFallback();
  SystemClockDriver* AsSystemClockDriver() override { return this; }

  // Those are only modified (after initialization) on the graph thread. The
  // graph thread does not run during the initialization.
  TimeStamp mInitialTimeStamp;
  TimeStamp mCurrentTimeStamp;
  TimeStamp mLastTimeStamp;

  // This is true if this SystemClockDriver runs the graph because we could not
  // open an audio stream.
  bool mIsFallback;

 * An OfflineClockDriver runs the graph as fast as possible, without waiting
 * between iteration.
class OfflineClockDriver : public ThreadedDriver {
  OfflineClockDriver(MediaStreamGraphImpl* aGraphImpl, GraphTime aSlice);
  virtual ~OfflineClockDriver();
  TimeDuration WaitInterval() override;
  MediaTime GetIntervalForIteration() override;
  OfflineClockDriver* AsOfflineClockDriver() override { return this; }

  // Time, in GraphTime, for each iteration
  GraphTime mSlice;

struct StreamAndPromiseForOperation {
  StreamAndPromiseForOperation(MediaStream* aStream, void* aPromise,
                               dom::AudioContextOperation aOperation,
                               dom::AudioContextOperationFlags aFlags);
  RefPtr<MediaStream> mStream;
  void* mPromise;
  dom::AudioContextOperation mOperation;
  dom::AudioContextOperationFlags mFlags;

enum AsyncCubebOperation { INIT, SHUTDOWN };

 * This is a graph driver that is based on callback functions called by the
 * audio api. This ensures minimal audio latency, because it means there is no
 * buffering happening: the audio is generated inside the callback.
 * This design is less flexible than running our own thread:
 * - We have no control over the thread:
 * - It cannot block, and it has to run for a shorter amount of time than the
 *   buffer it is going to fill, or an under-run is going to occur (short burst
 *   of silence in the final audio output).
 * - We can't know for sure when the callback function is going to be called
 *   (although we compute an estimation so we can schedule video frames)
 * - Creating and shutting the thread down is a blocking operation, that can
 *   take _seconds_ in some cases (because IPC has to be set up, and
 *   sometimes hardware components are involved and need to be warmed up)
 * - We have no control on how much audio we generate, we have to return exactly
 *   the number of frames asked for by the callback. Since for the Web Audio
 *   API, we have to do block processing at 128 frames per block, we need to
 *   keep a little spill buffer to store the extra frames.
class AudioCallbackDriver : public GraphDriver,
                            public MixerCallbackReceiver
#if defined(XP_WIN)
                            public audio::DeviceChangeListener
  /** If aInputChannelCount is zero, then this driver is output-only. */
  AudioCallbackDriver(MediaStreamGraphImpl* aGraphImpl,
                      uint32_t aInputChannelCount);
  virtual ~AudioCallbackDriver();

  void Start() override;
  void Revive() override;
  void WaitForNextIteration() override;
  void WakeUp() override;
  void Shutdown() override;
#if defined(XP_WIN)
  void ResetDefaultDevice() override;

  /* Static wrapper function cubeb calls back. */
  static long DataCallback_s(cubeb_stream* aStream, void* aUser,
                             const void* aInputBuffer, void* aOutputBuffer,
                             long aFrames);
  static void StateCallback_s(cubeb_stream* aStream, void* aUser,
                              cubeb_state aState);
  static void DeviceChangedCallback_s(void* aUser);
  /* This function is called by the underlying audio backend when a refill is
   * needed. This is what drives the whole graph when it is used to output
   * audio. If the return value is exactly aFrames, this function will get
   * called again. If it is less than aFrames, the stream will go in draining
   * mode, and this function will not be called again. */
  long DataCallback(const AudioDataValue* aInputBuffer,
                    AudioDataValue* aOutputBuffer, long aFrames);
  /* This function is called by the underlying audio backend, but is only used
   * for informational purposes at the moment. */
  void StateCallback(cubeb_state aState);
  /* This is an approximation of the number of millisecond there are between two
   * iterations of the graph. */
  uint32_t IterationDuration() override;

  /* This function gets called when the graph has produced the audio frames for
   * this iteration. */
  void MixerCallback(AudioDataValue* aMixedBuffer, AudioSampleFormat aFormat,
                     uint32_t aChannels, uint32_t aFrames,
                     uint32_t aSampleRate) override;

  AudioCallbackDriver* AsAudioCallbackDriver() override { return this; }

  uint32_t OutputChannelCount() {
    MOZ_ASSERT(mOutputChannels != 0 && mOutputChannels <= 8);
    return mOutputChannels;

  uint32_t InputChannelCount() { return mInputChannelCount; }

  /* Enqueue a promise that is going to be resolved when a specific operation
   * occurs on the cubeb stream. */
  void EnqueueStreamAndPromiseForOperation(
      MediaStream* aStream, void* aPromise,
      dom::AudioContextOperation aOperation,
      dom::AudioContextOperationFlags aFlags);

  std::thread::id ThreadId() { return mAudioThreadId.load(); }

  bool OnThread() override {
    return mAudioThreadId.load() == std::this_thread::get_id();

  bool ThreadRunning() override { return mAudioThreadRunning; }

  /* Whether the underlying cubeb stream has been started. See comment for
   * mStarted for details. */
  bool IsStarted();

  void CompleteAudioContextOperations(AsyncCubebOperation aOperation);

  /* Remove Mixer callbacks when switching */
  void RemoveMixerCallback();
  /* Add this driver in Mixer callbacks. */
  void AddMixerCallback();
   * On certain MacBookPro, the microphone is located near the left speaker.
   * We need to pan the sound output to the right speaker if we are using the
   * mic and the built-in speaker, or we will have terrible echo.  */
  void PanOutputIfNeeded(bool aMicrophoneActive);
   * This is called when the output device used by the cubeb stream changes. */
  void DeviceChangedCallback();
  /* Start the cubeb stream */
  bool StartStream();
  friend class AsyncCubebTask;
  bool Init();
  void Stop();
   *  Fall back to a SystemClockDriver using a normal thread. If needed,
   *  the graph will try to re-open an audio stream later. */
  void FallbackToSystemClockDriver();

  /* This is true when the method is executed on CubebOperation thread pool. */
  bool OnCubebOperationThread() {
    return mInitShutdownThread->IsOnCurrentThreadInfallible();

  /* MediaStreamGraphs are always down/up mixed to output channels. */
  uint32_t mOutputChannels;
  /* The size of this buffer comes from the fact that some audio backends can
   * call back with a number of frames lower than one block (128 frames), so we
   * need to keep at most two block in the SpillBuffer, because we always round
   * up to block boundaries during an iteration.
   * This is only ever accessed on the audio callback thread. */
  SpillBuffer<AudioDataValue, WEBAUDIO_BLOCK_SIZE * 2> mScratchBuffer;
  /* Wrapper to ensure we write exactly the number of frames we need in the
   * audio buffer cubeb passes us. This is only ever accessed on the audio
   * callback thread. */
  AudioCallbackBufferWrapper<AudioDataValue> mBuffer;
  /* cubeb stream for this graph. This is guaranteed to be non-null after Init()
   * has been called, and is synchronized internaly. */
  nsAutoRef<cubeb_stream> mAudioStream;
  /* The sample rate for the aforementionned cubeb stream. This is set on
   * initialization and can be read safely afterwards. */
  uint32_t mSampleRate;
  /* The number of input channels from cubeb. Set before opening cubeb. If it is
   * zero then the driver is output-only. */
  const uint32_t mInputChannelCount;
  /* Approximation of the time between two callbacks. This is used to schedule
   * video frames. This is in milliseconds. Only even used (after
   * inizatialization) on the audio callback thread. */
  uint32_t mIterationDurationMS;
  /* cubeb_stream_init calls the audio callback to prefill the buffers. The
   * previous driver has to be kept alive until the audio stream has been
   * started, because it is responsible to call cubeb_stream_start, so we delay
   * the cleanup of the previous driver until it has started the audio stream.
   * Otherwise, there is a race where we kill the previous driver thread
   * between cubeb_stream_init and cubeb_stream_start,
   * and callbacks after the prefill never get called.
   * This is written on the previous driver's thread (if switching) or main
   * thread (if this driver is the first one).
   * This is read on previous driver's thread (during callbacks from
   * cubeb_stream_init) and the audio thread (when switching away from this
   * driver back to a SystemClockDriver).
   * This is synchronized by the Graph's monitor.
   * */
  Atomic<bool> mStarted;

  struct AutoInCallback {
    explicit AutoInCallback(AudioCallbackDriver* aDriver);
    AudioCallbackDriver* mDriver;

  /* Shared thread pool with up to one thread for off-main-thread
   * initialization and shutdown of the audio stream via AsyncCubebTask. */
  const RefPtr<SharedThreadPool> mInitShutdownThread;
  /* This must be accessed with the graph monitor held. */
  AutoTArray<StreamAndPromiseForOperation, 1> mPromisesForOperation;
  /* This is used to signal adding the mixer callback on first run
   * of audio callback. This is atomic because it is touched from different
   * threads, the audio callback thread and the state change thread. However,
   * the order of the threads does not allow concurent access. */
  Atomic<bool> mAddedMixer;

  /* Contains the id of the audio thread for as long as the callback
   * is taking place, after that it is reseted to an invalid value. */
  std::atomic<std::thread::id> mAudioThreadId;
  /* True when audio thread is running. False before
   * starting and after stopping it the audio thread. */
  Atomic<bool> mAudioThreadRunning;
  /* Indication of whether a fallback SystemClockDriver should be started if
   * StateCallback() receives an error.  No mutex need be held during access.
   * The transition to true happens before cubeb_stream_start() is called.
   * After transitioning to false on the last DataCallback(), the stream is
   * not accessed from another thread until the graph thread either signals
   * main thread cleanup or dispatches an event to switch to another
   * driver. */
  bool mShouldFallbackIfError;
  /* True if this driver was created from a driver created because of a previous
   * AudioCallbackDriver failure. */
  bool mFromFallback;

class AsyncCubebTask : public Runnable {
  AsyncCubebTask(AudioCallbackDriver* aDriver, AsyncCubebOperation aOperation);

  nsresult Dispatch(uint32_t aFlags = NS_DISPATCH_NORMAL) {
    return mDriver->mInitShutdownThread->Dispatch(this, aFlags);

  virtual ~AsyncCubebTask();

  NS_IMETHOD Run() final;

  RefPtr<AudioCallbackDriver> mDriver;
  AsyncCubebOperation mOperation;
  RefPtr<MediaStreamGraphImpl> mShutdownGrip;

}  // namespace mozilla

#endif  // GRAPHDRIVER_H_