Media element resource selection algorithm should "await a stable state"

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
index 4b0c964be78172ce5cc7eae3c9642c835a39a006..43456ef4690856abfbbf77753312d3fe25e7f6d2 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -388,7 +388,7 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
     : HTMLElement(tagName, document)
     , ActiveScriptWrappable(this)
     , ActiveDOMObject(&document)
-    , m_loadTimer(this, &HTMLMediaElement::loadTimerFired)
+    , m_textTrackLoadTimer(this, &HTMLMediaElement::textTrackLoadTimerFired)
     , m_progressEventTimer(this, &HTMLMediaElement::progressEventTimerFired)
     , m_playbackProgressTimer(this, &HTMLMediaElement::playbackProgressTimerFired)
     , m_audioTracksTimer(this, &HTMLMediaElement::audioTracksTimerFired)
@@ -413,7 +413,6 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
     , m_displayMode(Unknown)
     , m_cachedTime(std::numeric_limits<double>::quiet_NaN())
     , m_fragmentEndTime(std::numeric_limits<double>::quiet_NaN())
-    , m_pendingActionFlags(0)
     , m_lockedPendingUserGesture(false)
     , m_playing(false)
     , m_shouldDelayLoadEvent(false)
@@ -436,6 +435,8 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
     , m_textTracks(nullptr)
     , m_playPromiseResolveTask(CancellableTaskFactory::create(this, &HTMLMediaElement::resolveScheduledPlayPromises))
     , m_playPromiseRejectTask(CancellableTaskFactory::create(this, &HTMLMediaElement::rejectScheduledPlayPromises))
+    , m_resourceSelectionAlgorithmContinuationTask(CancellableTaskFactory::create(this, &HTMLMediaElement::continueResourceSelectionAlgorithm))
+    , m_loadNextSourceChildAfterErrorTask(CancellableTaskFactory::create(this, &HTMLMediaElement::loadNextSourceChildAfterError))
     , m_audioSourceNode(nullptr)
     , m_autoplayHelperClient(AutoplayHelperClientImpl::create(this))
     , m_autoplayHelper(AutoplayExperimentHelper::create(m_autoplayHelperClient.get()))
@@ -635,17 +636,8 @@ void HTMLMediaElement::scheduleTextTrackResourceLoad()
 {
     BLINK_MEDIA_LOG << "scheduleTextTrackResourceLoad(" << (void*)this << ")";
 
-    m_pendingActionFlags |= LoadTextTrackResource;
-
-    if (!m_loadTimer.isActive())
-        m_loadTimer.startOneShot(0, BLINK_FROM_HERE);
-}
-
-void HTMLMediaElement::scheduleNextSourceChild()
-{
-    // Schedule the timer to try the next <source> element WITHOUT resetting state ala invokeLoadAlgorithm.
-    m_pendingActionFlags |= LoadMediaResource;
-    m_loadTimer.startOneShot(0, BLINK_FROM_HERE);
+    if (!m_textTrackLoadTimer.isActive())
+        m_textTrackLoadTimer.startOneShot(0, BLINK_FROM_HERE);
 }
 
 void HTMLMediaElement::scheduleEvent(const AtomicString& eventName)
@@ -661,19 +653,10 @@ void HTMLMediaElement::scheduleEvent(Event* event)
     m_asyncEventQueue->enqueueEvent(event);
 }
 
-void HTMLMediaElement::loadTimerFired(TimerBase*)
+void HTMLMediaElement::textTrackLoadTimerFired(TimerBase*)
 {
-    if (m_pendingActionFlags & LoadTextTrackResource)
-        honorUserPreferencesForAutomaticTextTrackSelection();
-
-    if (m_pendingActionFlags & LoadMediaResource) {
-        if (m_loadState == LoadingFromSourceElement)
-            loadNextSourceChild();
-        else
-            loadInternal();
-    }
-
-    m_pendingActionFlags = 0;
+    BLINK_MEDIA_LOG << "HTMLMediaElement::textTrackLoadTimerFired(" << (void*)this << ")";
+    honorUserPreferencesForAutomaticTextTrackSelection();
 }
 
 MediaError* HTMLMediaElement::error() const
@@ -741,15 +724,14 @@ void HTMLMediaElement::invokeLoadAlgorithm()
 
     // Perform the cleanup required for the resource load algorithm to run.
     stopPeriodicTimers();
-    m_loadTimer.stop();
     cancelDeferredLoad();
-    // FIXME: Figure out appropriate place to reset LoadTextTrackResource if necessary and set m_pendingActionFlags to 0 here.
-    m_pendingActionFlags &= ~LoadMediaResource;
     m_sentStalledEvent = false;
     m_haveFiredLoadedData = false;
     m_displayMode = Unknown;
 
     // 1 - Abort any already-running instance of the resource selection algorithm for this element.
+    m_resourceSelectionAlgorithmContinuationTask->cancel();
+    m_loadNextSourceChildAfterErrorTask->cancel();
     m_loadState = WaitingForSource;
     m_currentSourceNode = nullptr;
 
@@ -870,9 +852,13 @@ void HTMLMediaElement::invokeResourceSelectionAlgorithm()
         mediaControls()->reset();
 
     // 4 - Await a stable state, allowing the task that invoked this algorithm to continue
-    // TODO(srirama.m): Remove scheduleNextSourceChild() and post a microtask instead.
-    // See http://crbug.com/593289 for more details.
-    scheduleNextSourceChild();
+    Platform::current()->currentThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, m_resourceSelectionAlgorithmContinuationTask->cancelAndCreate());

[foolip, 2016/09/02 10:31:00]

Just to be clear, this and the below use of
Platform::current()->currentThread()->getWebTaskRunner()->postTask are both
places where I think we should either switch to the correct microtask timing,
and that using task timing in the interim creates the risk of getting stuck with
that timing for a long time instead.

+}
+
+void HTMLMediaElement::continueResourceSelectionAlgorithm()
+{
+    BLINK_MEDIA_LOG << "HTMLMediaElement::continueResourceSelectionAlgorithm(" << (void*)this << ")";
+    loadInternal();
 }
 
 void HTMLMediaElement::loadInternal()
@@ -1002,6 +988,13 @@ void HTMLMediaElement::loadNextSourceChild()
     loadResource(WebMediaPlayerSource(WebURL(mediaURL)), contentType);
 }
 
+void HTMLMediaElement::loadNextSourceChildAfterError()
+{
+    // 9.Otherwise.11 - Forget the media element's media-resource-specific tracks.
+    forgetResourceSpecificTracks();
+    loadNextSourceChild();
+}
+
 void HTMLMediaElement::loadResource(const WebMediaPlayerSource& source, const ContentType& contentType)
 {
     DCHECK(isMainThread());
@@ -1440,13 +1433,9 @@ void HTMLMediaElement::mediaLoadingFailed(WebMediaPlayer::NetworkState error)
             BLINK_MEDIA_LOG << "setNetworkState(" << (void*)this << ") - error event not sent, <source> was removed";
 
         // 9.Otherwise.10 - Asynchronously await a stable state. The synchronous section consists of all the remaining steps of this algorithm until the algorithm says the synchronous section has ended.
-
-        // 9.Otherwise.11 - Forget the media element's media-resource-specific tracks.
-        forgetResourceSpecificTracks();
-
         if (havePotentialSourceChild()) {
             BLINK_MEDIA_LOG << "setNetworkState(" << (void*)this << ") - scheduling next <source>";
-            scheduleNextSourceChild();
+            Platform::current()->currentThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, m_loadNextSourceChildAfterErrorTask->cancelAndCreate());
         } else {
             BLINK_MEDIA_LOG << "setNetworkState(" << (void*)this << ") - no more <source> elements, waiting";
             waitForSourceChange();
@@ -2855,7 +2844,7 @@ void HTMLMediaElement::sourceWasAdded(HTMLSourceElement* source)
 
     // 25. Jump back to the find next candidate step above.
     m_nextChildNodeToConsider = source;
-    scheduleNextSourceChild();
+    loadNextSourceChild();
 }
 
 void HTMLMediaElement::sourceWasRemoved(HTMLSourceElement* source)
@@ -3203,9 +3192,8 @@ void HTMLMediaElement::clearMediaPlayer()
     }
 
     stopPeriodicTimers();
-    m_loadTimer.stop();
+    m_textTrackLoadTimer.stop();
 
-    m_pendingActionFlags = 0;
     m_loadState = WaitingForSource;
 
     // We can't cast if we don't have a media player.