[chromecast] Moves CastAudioOutputStream::Backend to CMA thread.

chromecast/media/audio/cast_audio_mixer.cc

Index: chromecast/media/audio/cast_audio_mixer.cc
diff --git a/chromecast/media/audio/cast_audio_mixer.cc b/chromecast/media/audio/cast_audio_mixer.cc
index 4d236a1cb9f9f37aba7eef50212ccaed8d4a2c54..a7ed6f5bc1682434c460ad263ea0374ca1d52f0b 100644
--- a/chromecast/media/audio/cast_audio_mixer.cc
+++ b/chromecast/media/audio/cast_audio_mixer.cc
@@ -4,7 +4,9 @@
 
 #include "chromecast/media/audio/cast_audio_mixer.h"
 
+#include "base/bind.h"
 #include "base/logging.h"
+#include "base/memory/ptr_util.h"
 #include "chromecast/media/audio/cast_audio_manager.h"
 #include "chromecast/media/audio/cast_audio_output_stream.h"
 #include "media/base/audio_timestamp_helper.h"
@@ -21,30 +23,34 @@ namespace media {
 
 class CastAudioMixer::MixerProxyStream
     : public ::media::AudioOutputStream,
-      private ::media::AudioConverter::InputCallback {
+      public ::media::AudioConverter::InputCallback {
  public:
   MixerProxyStream(const ::media::AudioParameters& input_params,
                    const ::media::AudioParameters& output_params,
-                   CastAudioManager* audio_manager,
                    CastAudioMixer* audio_mixer)
-      : audio_manager_(audio_manager),
-        audio_mixer_(audio_mixer),
-        source_callback_(nullptr),
+      : audio_mixer_(audio_mixer),
         input_params_(input_params),
         output_params_(output_params),
         opened_(false),
-        volume_(1.0) {}
+        volume_(1.0),
+        source_callback_(nullptr) {
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
+  }
 
-  ~MixerProxyStream() override {}
+  ~MixerProxyStream() override {
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
+  }
 
   void OnError() {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
-
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
     if (source_callback_)
       source_callback_->OnError();
   }
 
  private:
+  // ResamplerProxy is an intermediate filter between MixerProxyStream and
+  // CastAudioMixer::output_stream_ whose only responsibility is to resample
+  // audio to the sample rate expected by CastAudioMixer::output_stream_.
   class ResamplerProxy : public ::media::AudioConverter::InputCallback {
    public:
     ResamplerProxy(::media::AudioConverter::InputCallback* input_callback,
@@ -53,6 +59,7 @@ class CastAudioMixer::MixerProxyStream
       resampler_.reset(
           new ::media::AudioConverter(input_params, output_params, false));
       resampler_->AddInput(input_callback);
+      DETACH_FROM_THREAD(backend_thread_checker_);
     }
 
     ~ResamplerProxy() override {}
@@ -61,20 +68,21 @@ class CastAudioMixer::MixerProxyStream
     // ::media::AudioConverter::InputCallback implementation
     double ProvideInput(::media::AudioBus* audio_bus,
                         uint32_t frames_delayed) override {
+      DCHECK_CALLED_ON_VALID_THREAD(backend_thread_checker_);
       resampler_->ConvertWithDelay(frames_delayed, audio_bus);
-
       // Volume multiplier has already been applied by |resampler_|.
       return 1.0;
     }
 
     std::unique_ptr<::media::AudioConverter> resampler_;
 
+    THREAD_CHECKER(backend_thread_checker_);
     DISALLOW_COPY_AND_ASSIGN(ResamplerProxy);
   };
 
   // ::media::AudioOutputStream implementation
   bool Open() override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
     ::media::AudioParameters::Format format = input_params_.format();
     DCHECK((format == ::media::AudioParameters::AUDIO_PCM_LINEAR) ||
@@ -93,46 +101,52 @@ class CastAudioMixer::MixerProxyStream
   }
 
   void Close() override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
     if (proxy_)
       Stop();
     if (opened_)
       audio_mixer_->Unregister(this);
+
     // Signal to the manager that we're closed and can be removed.
     // This should be the last call in the function as it deletes "this".
-    audio_manager_->ReleaseOutputStream(this);
+    audio_mixer_->audio_manager_->ReleaseOutputStream(this);
   }
 
   void Start(AudioSourceCallback* source_callback) override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
     DCHECK(source_callback);
 
     if (!opened_ || proxy_)
       return;
     source_callback_ = source_callback;
-    proxy_.reset(new ResamplerProxy(this, input_params_, output_params_));
+    proxy_ =
+        base::MakeUnique<ResamplerProxy>(this, input_params_, output_params_);
     audio_mixer_->AddInput(proxy_.get());
   }
 
   void Stop() override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
     if (!proxy_)
       return;
     audio_mixer_->RemoveInput(proxy_.get());
+    // Once the above function returns it is guaranteed that proxy_ or
+    // source_callback_ would not be used on the backend thread, so it is safe
+    // to reset them.
     proxy_.reset();
     source_callback_ = nullptr;
   }
 
   void SetVolume(double volume) override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
+    base::AutoLock auto_lock(volume_lock_);
     volume_ = volume;
   }
 
   void GetVolume(double* volume) override {
-    DCHECK(audio_manager_->GetTaskRunner()->BelongsToCurrentThread());
+    DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
     *volume = volume_;
   }
@@ -140,56 +154,57 @@ class CastAudioMixer::MixerProxyStream
   // ::media::AudioConverter::InputCallback implementation
   double ProvideInput(::media::AudioBus* audio_bus,
                       uint32_t frames_delayed) override {
+    // Called on backend thread. Member variables accessed from both backend
+    // and audio thread must be thread-safe.
     DCHECK(source_callback_);
 
     const base::TimeDelta delay = ::media::AudioTimestampHelper::FramesToTime(
         frames_delayed, input_params_.sample_rate());
     source_callback_->OnMoreData(delay, base::TimeTicks::Now(), 0, audio_bus);
+
+    base::AutoLock auto_lock(volume_lock_);
     return volume_;
   }
 
-  CastAudioManager* const audio_manager_;
   CastAudioMixer* const audio_mixer_;
-
-  std::unique_ptr<ResamplerProxy> proxy_;
-  AudioSourceCallback* source_callback_;
   const ::media::AudioParameters input_params_;
   const ::media::AudioParameters output_params_;
+
   bool opened_;
   double volume_;
+  base::Lock volume_lock_;
+  AudioSourceCallback* source_callback_;
+  std::unique_ptr<ResamplerProxy> proxy_;
 
+  THREAD_CHECKER(audio_thread_checker_);
   DISALLOW_COPY_AND_ASSIGN(MixerProxyStream);
 };
 
-CastAudioMixer::CastAudioMixer(const RealStreamFactory& real_stream_factory)
-    : error_(false),
-      real_stream_factory_(real_stream_factory),
-      output_stream_(nullptr) {
+CastAudioMixer::CastAudioMixer(CastAudioManager* audio_manager)
+    : audio_manager_(audio_manager), error_(false), output_stream_(nullptr) {
   output_params_ = ::media::AudioParameters(
       ::media::AudioParameters::Format::AUDIO_PCM_LOW_LATENCY,
       ::media::CHANNEL_LAYOUT_STEREO, kSampleRate, kBitsPerSample,
       kFramesPerBuffer);
   mixer_.reset(
       new ::media::AudioConverter(output_params_, output_params_, false));
-  thread_checker_.DetachFromThread();
+  DETACH_FROM_THREAD(audio_thread_checker_);
 }
 
 CastAudioMixer::~CastAudioMixer() {}
 
 ::media::AudioOutputStream* CastAudioMixer::MakeStream(
-    const ::media::AudioParameters& params,
-    CastAudioManager* audio_manager) {
-  return new MixerProxyStream(params, output_params_, audio_manager, this);
+    const ::media::AudioParameters& params) {
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
+  return new MixerProxyStream(params, output_params_, this);
 }
 
 bool CastAudioMixer::Register(MixerProxyStream* proxy_stream) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
   DCHECK(std::find(proxy_streams_.begin(), proxy_streams_.end(),
                    proxy_stream) == proxy_streams_.end());
 
-  // If the mixer is in an error state, do not allow any new
-  // registrations until every active stream has been
-  // unregistered.
+  // Do not allow opening new streams while in error state.
   if (error_)
     return false;
 
@@ -198,7 +213,7 @@ bool CastAudioMixer::Register(MixerProxyStream* proxy_stream) {
   // is not opened properly.
   if (proxy_streams_.empty()) {
     DCHECK(!output_stream_);
-    output_stream_ = real_stream_factory_.Run(output_params_);
+    output_stream_ = audio_manager_->MakeMixerOutputStream(output_params_);
     if (!output_stream_->Open()) {
       output_stream_->Close();
       output_stream_ = nullptr;
@@ -206,17 +221,16 @@ bool CastAudioMixer::Register(MixerProxyStream* proxy_stream) {
     }
   }
 
-  proxy_streams_.push_back(proxy_stream);
+  proxy_streams_.insert(proxy_stream);
   return true;
 }
 
 void CastAudioMixer::Unregister(MixerProxyStream* proxy_stream) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-  auto it =
-      std::find(proxy_streams_.begin(), proxy_streams_.end(), proxy_stream);
-  DCHECK(it != proxy_streams_.end());
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
+  DCHECK(std::find(proxy_streams_.begin(), proxy_streams_.end(),
+                   proxy_stream) != proxy_streams_.end());
 
-  proxy_streams_.erase(it);
+  proxy_streams_.erase(proxy_stream);
 
   // Reset the state once all streams have been unregistered.
   if (proxy_streams_.empty()) {
@@ -230,19 +244,25 @@ void CastAudioMixer::Unregister(MixerProxyStream* proxy_stream) {
 
 void CastAudioMixer::AddInput(
     ::media::AudioConverter::InputCallback* input_callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
   // Start the backend if there are no current inputs.
   if (mixer_->empty() && output_stream_)
     output_stream_->Start(this);
+
+  base::AutoLock auto_lock(mixer_lock_);
   mixer_->AddInput(input_callback);
 }
 
 void CastAudioMixer::RemoveInput(
     ::media::AudioConverter::InputCallback* input_callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
+
+  {
+    base::AutoLock auto_lock(mixer_lock_);
+    mixer_->RemoveInput(input_callback);
+  }
 
-  mixer_->RemoveInput(input_callback);
   // Stop |output_stream_| if there are no inputs and the stream is running.
   if (mixer_->empty() && output_stream_)
     output_stream_->Stop();
@@ -252,36 +272,28 @@ int CastAudioMixer::OnMoreData(base::TimeDelta delay,
                                base::TimeTicks /* delay_timestamp */,
                                int /* prior_frames_skipped */,
                                ::media::AudioBus* dest) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
+  // Called on backend thread.
   uint32_t frames_delayed = ::media::AudioTimestampHelper::TimeToFrames(
       delay, output_params_.sample_rate());
+
+  base::AutoLock auto_lock(mixer_lock_);
   mixer_->ConvertWithDelay(frames_delayed, dest);
   return dest->frames();
 }
 
 void CastAudioMixer::OnError() {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
-  // TODO(ameyak): Add rate limiting. If errors are seen to occur
-  //               above some arbitrary value in a specified amount
-  //               of time, signal errors to all currently active
-  //               streams and close.
+  // Called on backend thread.
+  audio_manager_->GetTaskRunner()->PostTask(
+      FROM_HERE,
+      base::BindOnce(&CastAudioMixer::HandleError, base::Unretained(this)));
+}
 
-  output_stream_->Stop();
-  output_stream_->Close();
-  output_stream_ = real_stream_factory_.Run(output_params_);
+void CastAudioMixer::HandleError() {
+  DCHECK_CALLED_ON_VALID_THREAD(audio_thread_checker_);
 
-  if (output_stream_->Open()) {
-    output_stream_->Start(this);
-  } else {
-    // Assume error state
-    output_stream_->Close();
-    output_stream_ = nullptr;
-    error_ = true;
-    for (auto it = proxy_streams_.begin(); it != proxy_streams_.end(); it++)
-      (*it)->OnError();
-  }
+  error_ = true;
+  for (auto it = proxy_streams_.begin(); it != proxy_streams_.end(); ++it)
+    (*it)->OnError();
 }
 
 }  // namespace media