Implement one-shot audio focus inside MediaSession

content/browser/media/session/media_session_impl.cc

 // Copyright 2015 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.
 
 #include "content/browser/media/session/media_session_impl.h"
 
 #include "content/browser/media/session/audio_focus_delegate.h"
 #include "content/browser/media/session/media_session_player_observer.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 47 matching lines @@
   if (!session) {
     CreateForWebContents(web_contents);
     session = FromWebContents(web_contents);
     session->Initialize();
   }
   return session;
 }
 
 MediaSessionImpl::~MediaSessionImpl() {
   DCHECK(players_.empty());
+  DCHECK(pepper_players_.empty());
+  DCHECK(one_shot_players_.empty());
   DCHECK(audio_focus_state_ == State::INACTIVE);
   for (auto& observer : observers_)
     observer.MediaSessionDestroyed();
 }
 
 void MediaSessionImpl::WebContentsDestroyed() {
   // This should only work for tests. In production, all the players should have
   // already been removed before WebContents is destroyed.
 
   // TODO(zqzhang): refactor MediaSessionImpl, maybe move the interface used to
@@ skipping 16 matching lines @@
 void MediaSessionImpl::SetMetadata(
     const base::Optional<MediaMetadata>& metadata) {
   metadata_ = metadata;
   for (auto& observer : observers_)
     observer.MediaSessionMetadataChanged(metadata);
 }
 
 bool MediaSessionImpl::AddPlayer(MediaSessionPlayerObserver* observer,
                                  int player_id,
                                  media::MediaContentType media_content_type) {
-  if (media_content_type == media::MediaContentType::Uncontrollable)
-    return true;
+  if (media_content_type == media::MediaContentType::OneShot)
+    return AddOneShotPlayer(observer, player_id);
   if (media_content_type == media::MediaContentType::Pepper)
     return AddPepperPlayer(observer, player_id);
 
   observer->OnSetVolumeMultiplier(player_id, GetVolumeMultiplier());
 
-  // Determine the audio focus type required for playing the new player.
-  // TODO(zqzhang): handle duckable and uncontrollable.
-  // See https://crbug.com/639277.
   AudioFocusManager::AudioFocusType required_audio_focus_type;
   if (media_content_type == media::MediaContentType::Persistent) {
     required_audio_focus_type = AudioFocusManager::AudioFocusType::Gain;
   } else {
     required_audio_focus_type =
         AudioFocusManager::AudioFocusType::GainTransientMayDuck;
   }
 
   // If the audio focus is already granted and is of type Content, there is
   // nothing to do. If it is granted of type Transient the requested type is
@@ skipping 11 matching lines @@
 
   if (audio_focus_state_ != State::ACTIVE)
     return false;
 
   // The session should be reset if a player is starting while all players are
   // suspended.
   if (old_audio_focus_state != State::ACTIVE)
     players_.clear();
 
   players_.insert(PlayerIdentifier(observer, player_id));
-  UpdateWebContents();
+  DispatchStateChange();
 
   return true;
 }
 
 void MediaSessionImpl::RemovePlayer(MediaSessionPlayerObserver* observer,
                                     int player_id) {
   auto it = players_.find(PlayerIdentifier(observer, player_id));
   if (it != players_.end())
     players_.erase(it);
 
   it = pepper_players_.find(PlayerIdentifier(observer, player_id));
   if (it != pepper_players_.end())
     pepper_players_.erase(it);
 
+  it = one_shot_players_.find(PlayerIdentifier(observer, player_id));
+  if (it != one_shot_players_.end()) {
+    one_shot_players_.erase(it);
+
+    // The session may become controllable after all one-shot players are
+    // removed.
+    if (one_shot_players_.empty())
+      DispatchStateChange();
+  }
+
   AbandonSystemAudioFocusIfNeeded();
 }
 
 void MediaSessionImpl::RemovePlayers(MediaSessionPlayerObserver* observer) {
   for (auto it = players_.begin(); it != players_.end();) {
     if (it->observer == observer)
       players_.erase(it++);
     else
       ++it;
   }
 
   for (auto it = pepper_players_.begin(); it != pepper_players_.end();) {
     if (it->observer == observer)
       pepper_players_.erase(it++);
     else
       ++it;
   }
 
+  for (auto it = one_shot_players_.begin(); it != one_shot_players_.end();) {
+    if (it->observer == observer)
+      one_shot_players_.erase(it++);
+    else
+      ++it;
+
+    // The session may become controllable after all one-shot players are
+    // removed.
+    if (one_shot_players_.empty())
+      DispatchStateChange();
+  }
+
   AbandonSystemAudioFocusIfNeeded();
 }
 
 void MediaSessionImpl::RecordSessionDuck() {
   uma_helper_.RecordSessionSuspended(
       MediaSessionSuspendedSource::SystemTransientDuck);
 }
 
 void MediaSessionImpl::OnPlayerPaused(MediaSessionPlayerObserver* observer,
                                       int player_id) {
   // If a playback is completed, BrowserMediaPlayerManager will call
   // OnPlayerPaused() after RemovePlayer(). This is a workaround.
   // Also, this method may be called when a player that is not added
   // to this session (e.g. a silent video) is paused. MediaSessionImpl
   // should ignore the paused player for this case.
   if (!players_.count(PlayerIdentifier(observer, player_id)) &&
-      !pepper_players_.count(PlayerIdentifier(observer, player_id))) {
+      !pepper_players_.count(PlayerIdentifier(observer, player_id)) &&
+      !one_shot_players_.count(PlayerIdentifier(observer, player_id))) {
     return;
   }
 
   // If the player to be removed is a pepper player, or there is more than one
   // observer, remove the paused one from the session.
   if (pepper_players_.count(PlayerIdentifier(observer, player_id)) ||
       players_.size() != 1) {
     RemovePlayer(observer, player_id);
     return;
   }
 
+  // If the player is a one-shot player, just remove it since it is not expected
+  // to resume a one-shot player via resuming MediaSession.
+  if (one_shot_players_.count(PlayerIdentifier(observer, player_id))) {
+    RemovePlayer(observer, player_id);
+    return;
+  }
+
   // Otherwise, suspend the session.
   DCHECK(!IsSuspended());
   OnSuspendInternal(SuspendType::CONTENT, State::SUSPENDED);
 }
 
 void MediaSessionImpl::Resume(SuspendType suspend_type) {
   DCHECK(IsReallySuspended());
 
   // When the resume requests comes from another source than system, audio focus
   // must be requested.
@@ skipping 71 matching lines @@
   return audio_focus_state_ == State::SUSPENDED;
 }
 
 bool MediaSessionImpl::IsSuspended() const {
   // TODO(mlamouri): should be == State::SUSPENDED.
   return audio_focus_state_ != State::ACTIVE;
 }
 
 bool MediaSessionImpl::IsControllable() const {
   // Only media session having focus Gain can be controllable unless it is
-  // inactive.
+  // inactive. Also, the session will be uncontrollable if it contains one-shot
+  // players.
   return audio_focus_state_ != State::INACTIVE &&
-         audio_focus_type_ == AudioFocusManager::AudioFocusType::Gain;
+         audio_focus_type_ == AudioFocusManager::AudioFocusType::Gain &&
+         (one_shot_players_.empty());
 }
 
 bool MediaSessionImpl::HasPepper() const {
   return !pepper_players_.empty();
 }
 
 std::unique_ptr<base::CallbackList<void(MediaSessionImpl::State)>::Subscription>
 MediaSessionImpl::RegisterMediaSessionStateChangedCallbackForTest(
     const StateChangedCallback& cb) {
   return media_session_state_listeners_.Add(cb);
 }
 
 void MediaSessionImpl::SetDelegateForTests(
     std::unique_ptr<AudioFocusDelegate> delegate) {
   delegate_ = std::move(delegate);
 }
 
 bool MediaSessionImpl::IsActiveForTest() const {
   return audio_focus_state_ == State::ACTIVE;
 }
 
 MediaSessionUmaHelper* MediaSessionImpl::uma_helper_for_test() {
   return &uma_helper_;
 }
 
 void MediaSessionImpl::RemoveAllPlayersForTest() {
   players_.clear();
+  pepper_players_.clear();
+  one_shot_players_.clear();

[whywhat, 2016/11/03 14:32:17]

nit: I feel there's more code duplication here w.r.t. three collections of
players

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

Yeah, I feel this too. But as pepper_players_ is likely to go away, let's keep
it here.

   AbandonSystemAudioFocusIfNeeded();
 }
 
 void MediaSessionImpl::OnSuspendInternal(SuspendType suspend_type,
                                          State new_state) {
   DCHECK(!HasPepper());
 
   DCHECK(new_state == State::SUSPENDED || new_state == State::INACTIVE);
   // UI suspend cannot use State::INACTIVE.
   DCHECK(suspend_type == SuspendType::SYSTEM || new_state == State::SUSPENDED);
 
+  if (!one_shot_players_.empty())
+    return;
+
   if (audio_focus_state_ != State::ACTIVE)
     return;
 
   switch (suspend_type) {
     case SuspendType::UI:
       uma_helper_.RecordSessionSuspended(MediaSessionSuspendedSource::UI);
       break;
     case SuspendType::SYSTEM:
       switch (new_state) {
         case State::SUSPENDED:
@@ skipping 21 matching lines @@
     // SuspendType::CONTENT happens when the suspend action came from
     // the page in which case the player is already paused.
     // Otherwise, the players need to be paused.
     for (const auto& it : players_)
       it.observer->OnSuspend(it.player_id);
   }
 
   for (const auto& it : pepper_players_)
     it.observer->OnSetVolumeMultiplier(it.player_id, kDuckingVolumeMultiplier);
 
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
 void MediaSessionImpl::OnResumeInternal(SuspendType suspend_type) {
   if (suspend_type == SuspendType::SYSTEM && suspend_type_ != suspend_type)
     return;
 
   SetAudioFocusState(State::ACTIVE);
 
   for (const auto& it : players_)
     it.observer->OnResume(it.player_id);
 
   for (const auto& it : pepper_players_)
     it.observer->OnSetVolumeMultiplier(it.player_id, GetVolumeMultiplier());
 
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
 MediaSessionImpl::MediaSessionImpl(WebContents* web_contents)
     : WebContentsObserver(web_contents),
       audio_focus_state_(State::INACTIVE),
       audio_focus_type_(
           AudioFocusManager::AudioFocusType::GainTransientMayDuck),
       is_ducking_(false) {
 #if defined(OS_ANDROID)
   session_android_.reset(new MediaSessionAndroid(this));
@@ skipping 11 matching lines @@
 
   // MediaSessionImpl must change its state & audio focus type AFTER requesting
   // audio focus.
   SetAudioFocusState(result ? State::ACTIVE : State::INACTIVE);
   audio_focus_type_ = audio_focus_type;
   return result;
 }
 
 void MediaSessionImpl::AbandonSystemAudioFocusIfNeeded() {
   if (audio_focus_state_ == State::INACTIVE || !players_.empty() ||
-      !pepper_players_.empty()) {
+      !pepper_players_.empty() || !one_shot_players_.empty()) {
     return;
   }
   delegate_->AbandonAudioFocus();
 
   SetAudioFocusState(State::INACTIVE);
-  UpdateWebContents();
+  DispatchStateChange();
 }
 
-void MediaSessionImpl::UpdateWebContents() {
+void MediaSessionImpl::DispatchStateChange() {
   media_session_state_listeners_.Notify(audio_focus_state_);
   for (auto& observer : observers_)
     observer.MediaSessionStateChanged(IsControllable(), IsSuspended());
 }
 
 void MediaSessionImpl::SetAudioFocusState(State audio_focus_state) {
   if (audio_focus_state == audio_focus_state_)
     return;
 
   audio_focus_state_ = audio_focus_state;
@@ skipping 13 matching lines @@
 bool MediaSessionImpl::AddPepperPlayer(MediaSessionPlayerObserver* observer,
                                        int player_id) {
   bool success =
       RequestSystemAudioFocus(AudioFocusManager::AudioFocusType::Gain);
   DCHECK(success);
 
   pepper_players_.insert(PlayerIdentifier(observer, player_id));
 
   observer->OnSetVolumeMultiplier(player_id, GetVolumeMultiplier());
 
+  DispatchStateChange();
   return true;
 }
 
+bool MediaSessionImpl::AddOneShotPlayer(MediaSessionPlayerObserver* observer,
+                                        int player_id) {
+  // Don't check whether the request is successful or not. One-shot players
+  // should play uninterrupted.

[whywhat, 2016/11/03 14:32:16]

that means we'd play them even if the user is in the middle of a phone call? is
it intended?

[Zhiqiang Zhang (Slow), 2016/11/04 14:10:54]

OK, let's give a chance for the players to respond.

+  RequestSystemAudioFocus(AudioFocusManager::AudioFocusType::Gain);
+
+  one_shot_players_.insert(PlayerIdentifier(observer, player_id));
+
+  DispatchStateChange();
+  return true;
+}
+
 }  // namespace content