Refactor resource load and resource selection algorithms as per spec

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

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 314 matching lines @@
     , m_playing(false)
     , m_shouldDelayLoadEvent(false)
     , m_haveFiredLoadedData(false)
     , m_autoplaying(true)
     , m_muted(false)
     , m_paused(true)
     , m_seeking(false)
     , m_sentStalledEvent(false)
     , m_sentEndEvent(false)
     , m_closedCaptionsVisible(false)
-    , m_havePreparedToPlay(false)
+    , m_forceEffectivePreloadAuto(false)
     , m_tracksAreReady(true)
     , m_processingPreferenceChange(false)
     , m_remoteRoutesAvailable(false)
     , m_playingRemotely(false)
     , m_isFinalizing(false)
     , m_initialPlayWithoutUserGesture(false)
     , m_autoplayMediaCounted(false)
     , m_inOverlayFullscreenVideo(false)
     , m_audioTracks(AudioTrackList::create(*this))
     , m_videoTracks(VideoTrackList::create(*this))
@@ skipping 118 matching lines @@
 
     removeElementFromDocumentMap(this, &oldDocument);
     addElementToDocumentMap(this, &document());
 
     // FIXME: This is a temporary fix to prevent this object from causing the
     // MediaPlayer to dereference LocalFrame and FrameLoader pointers from the
     // previous document. This restarts the load, as if the src attribute had been set.
     // A proper fix would provide a mechanism to allow this object to refresh
     // the MediaPlayer's LocalFrame and FrameLoader references on
     // document changes so that playback can be resumed properly.
-    clearMediaPlayer(LoadMediaResource);
-    scheduleDelayedAction(LoadMediaResource);
+    invokeLoadAlgorithm();
 
     // Decrement the load event delay count on oldDocument now that m_webMediaPlayer has been destroyed
     // and there is no risk of dispatching a load event from within the destructor.
     oldDocument.decrementLoadEventDelayCount();
 
     ActiveDOMObject::didMoveToNewExecutionContext(&document());
     HTMLElement::didMoveToNewDocument(oldDocument);
 }
 
 bool HTMLMediaElement::supportsFocus() const
 {
     if (ownerDocument()->isMediaDocument())
         return false;
 
     // If no controls specified, we should still be able to focus the element if it has tabIndex.
     return shouldShowControls() || HTMLElement::supportsFocus();
 }
 
 bool HTMLMediaElement::isMouseFocusable() const
 {
     return false;
 }
 
 void HTMLMediaElement::parseAttribute(const QualifiedName& name, const AtomicString& oldValue, const AtomicString& value)
 {
     if (name == srcAttr) {
         // Trigger a reload, as long as the 'src' attribute is present.
         if (!value.isNull()) {
-            clearMediaPlayer(LoadMediaResource);
-            scheduleDelayedAction(LoadMediaResource);
+            invokeLoadAlgorithm();
         }
     } else if (name == controlsAttr) {
         UseCounter::count(document(), UseCounter::HTMLMediaElementControlsAttribute);
         configureMediaControls();
     } else if (name == preloadAttr) {
         setPlayerPreload();
     } else if (name == disableremoteplaybackAttr) {
         UseCounter::count(document(), UseCounter::DisableRemotePlaybackAttribute);
     } else {
         HTMLElement::parseAttribute(name, oldValue, value);
     }
 }
 
 void HTMLMediaElement::finishParsingChildren()
 {
     HTMLElement::finishParsingChildren();
 
     if (Traversal<HTMLTrackElement>::firstChild(*this))
-        scheduleDelayedAction(LoadTextTrackResource);
+        scheduleTextTrackResourceLoad();
 }
 
 bool HTMLMediaElement::layoutObjectIsNeeded(const ComputedStyle& style)
 {
     return shouldShowControls() && HTMLElement::layoutObjectIsNeeded(style);
 }
 
 LayoutObject* HTMLMediaElement::createLayoutObject(const ComputedStyle&)
 {
     return new LayoutMedia(this);
 }
 
 Node::InsertionNotificationRequest HTMLMediaElement::insertedInto(ContainerNode* insertionPoint)
 {
     WTF_LOG(Media, "HTMLMediaElement::insertedInto(%p, %p)", this, insertionPoint);
 
     HTMLElement::insertedInto(insertionPoint);
     if (insertionPoint->inDocument()) {
         UseCounter::count(document(), UseCounter::HTMLMediaElementInDocument);
         if (!getAttribute(srcAttr).isEmpty() && m_networkState == NETWORK_EMPTY)
-            scheduleDelayedAction(LoadMediaResource);
+            invokeLoadAlgorithm();
     }
 
     return InsertionShouldCallDidNotifySubtreeInsertions;
 }
 
 void HTMLMediaElement::didNotifySubtreeInsertionsToDocument()
 {
     configureMediaControls();
 }
 
@@ skipping 16 matching lines @@
     if (layoutObject())
         layoutObject()->updateFromElement();
 }
 
 void HTMLMediaElement::didRecalcStyle(StyleRecalcChange)
 {
     if (layoutObject())
         layoutObject()->updateFromElement();
 }
 
-void HTMLMediaElement::scheduleDelayedAction(DelayedActionType actionType)
+void HTMLMediaElement::scheduleTextTrackResourceLoad()
 {
-    WTF_LOG(Media, "HTMLMediaElement::scheduleDelayedAction(%p)", this);
+    WTF_LOG(Media, "HTMLMediaElement::scheduleTextTrackResourceLoad(%p)", this);
 
-    if ((actionType & LoadMediaResource) && !(m_pendingActionFlags & LoadMediaResource)) {
-        prepareForLoad();
-        m_pendingActionFlags |= LoadMediaResource;
-    }
-
-    if (actionType & LoadTextTrackResource)
-        m_pendingActionFlags |= LoadTextTrackResource;
+    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 prepareForLoad.
     m_pendingActionFlags |= LoadMediaResource;
     m_loadTimer.startOneShot(0, BLINK_FROM_HERE);
@@ skipping 100 matching lines @@
 
     if (UserGestureIndicator::processingUserGesture() && m_userGestureRequiredForPlay) {
         recordAutoplayMetric(AutoplayEnabledThroughLoad);
         m_userGestureRequiredForPlay = false;
         // While usergesture-initiated load()s technically count as autoplayed,
         // they don't feel like such to the users and hence we don't want to
         // count them for the purposes of metrics.
         m_autoplayMediaCounted = true;
     }
 
+    m_forceEffectivePreloadAuto = true;
+    invokeLoadAlgorithm();
+}
+
+void HTMLMediaElement::invokeLoadAlgorithm()
+{
+    WTF_LOG(Media, "HTMLMediaElement::invokeLoadAlgorithm(%p)", this);
+
     prepareForLoad();
-    loadInternal();
-    prepareToPlay();
+    scheduleNextSourceChild();
 }
 
 void HTMLMediaElement::prepareForLoad()
 {
     WTF_LOG(Media, "HTMLMediaElement::prepareForLoad(%p)", this);
 
     // 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_sentEndEvent = false;
     m_sentStalledEvent = false;
     m_haveFiredLoadedData = false;
-    m_havePreparedToPlay = false;

[philipj_slow, 2016/03/11 12:52:41]

Actually, the renamed state bit should also be reset here, otherwise it'll be
impossible to reuse a media element for a new load with preload=auto.  This
could be a problem in the current shape of load() because the
`m_forceEffectivePreloadAuto = true` before invokeLoadAlgorithm() is immediately
undone, but setting it after is too late. Once the resource selection algorithm
is async, however, the order shouldn't matter.

If necessary to get things working in the interim, maybe you can do
`m_forceEffectivePreloadAuto = false` before call to invokeLoadAlgorithm()
except the one in load(), with TODOs to move it into prepareForLoad() together
with the microtask fix?

[Srirama, 2016/03/11 14:58:20]

Done.

     m_displayMode = Unknown;
 
     // 1 - Abort any already-running instance of the resource selection algorithm for this element.
     m_loadState = WaitingForSource;
     m_currentSourceNode = nullptr;
 
     // 2 - If there are any tasks from the media element's media element event task source in
     // one of the task queues, then remove those tasks.
     cancelPendingEventsAndCallbacks();
 
@@ skipping 43 matching lines @@
     }
 
     // 5 - Set the playbackRate attribute to the value of the defaultPlaybackRate attribute.
     setPlaybackRate(defaultPlaybackRate());
 
     // 6 - Set the error attribute to null and the autoplaying flag to true.
     m_error = nullptr;
     m_autoplaying = true;
 
     // 7 - Invoke the media element's resource selection algorithm.
+    invokeResourceSelectionAlgorithm();
 
     // 8 - Note: Playback of any previously playing media resource for this element stops.
+}
 
+void HTMLMediaElement::invokeResourceSelectionAlgorithm()
+{
+    WTF_LOG(Media, "HTMLMediaElement::invokeResourceSelectionAlgorithm(%p)", this);
     // The resource selection algorithm
     // 1 - Set the networkState to NETWORK_NO_SOURCE
     setNetworkState(NETWORK_NO_SOURCE);
 
-    // 2 - Asynchronously await a stable state.
+    // 2 - Set the element's show poster flag to true
+    // TODO(srirama.m): Introduce show poster flag and update it as per spec
 
     m_playedTimeRanges = TimeRanges::create();
 
     // FIXME: Investigate whether these can be moved into m_networkState != NETWORK_EMPTY block above
     // so they are closer to the relevant spec steps.
     m_lastSeekTime = 0;
     m_duration = std::numeric_limits<double>::quiet_NaN();
 
-    // The spec doesn't say to block the load event until we actually run the asynchronous section
-    // algorithm, but do it now because we won't start that until after the timer fires and the
-    // event may have already fired by then.
+    // 3 - Set the media element's delaying-the-load-event flag to true (this delays the load event)
     setShouldDelayLoadEvent(true);
     if (mediaControls())
         mediaControls()->reset();
+
+    // 4 - Await a stable state, allowing the task that invoked this algorithm to continue
+    // TODO(srirama.m): Schedule an async continuation of this algorithm as per the spec
 }
 
 void HTMLMediaElement::loadInternal()
 {
     // HTMLMediaElement::textTracksAreReady will need "... the text tracks whose mode was not in the
     // disabled state when the element's resource selection algorithm last started".
     m_textTracksWhenResourceSelectionBegan.clear();
     if (m_textTracks) {
         for (unsigned i = 0; i < m_textTracks->length(); ++i) {
             TextTrack* track = m_textTracks->anonymousIndexedGetter(i);
@@ skipping 142 matching lines @@
                     m_mediaSource = nullptr;
                     attemptLoad = false;
                 }
             }
         }
     }
 
     if (attemptLoad && canLoadURL(url, contentType)) {
         ASSERT(!webMediaPlayer());
 
-        if (!m_havePreparedToPlay && effectivePreloadType() == WebMediaPlayer::PreloadNone) {
+        if (effectivePreloadType() == WebMediaPlayer::PreloadNone) {
             WTF_LOG(Media, "HTMLMediaElement::loadResource(%p) : Delaying load because preload == 'none'", this);
             deferLoad();
         } else {
             startPlayerLoad();
         }
     } else {
         mediaLoadingFailed(WebMediaPlayer::NetworkStateFormatError);
     }
 
     // If there is no poster to display, allow the media engine to render video frames as soon as
@@ skipping 57 matching lines @@
         // This handles any transition to or from fullscreen overlay mode.
         frame->chromeClient().enterFullScreenForElement(this);
     }
 }
 
 void HTMLMediaElement::setPlayerPreload()
 {
     if (m_webMediaPlayer)
         m_webMediaPlayer->setPreload(effectivePreloadType());
 
-    if (loadIsDeferred() && preloadType() != WebMediaPlayer::PreloadNone)
+    if (loadIsDeferred() && effectivePreloadType() != WebMediaPlayer::PreloadNone)
         startDeferredLoad();
 }
 
 bool HTMLMediaElement::loadIsDeferred() const
 {
     return m_deferredLoadState != NotDeferred;
 }
 
 void HTMLMediaElement::deferLoad()
 {
@@ skipping 532 matching lines @@
     if (!m_playedTimeRanges)
         m_playedTimeRanges = TimeRanges::create();
     m_playedTimeRanges->add(start, end);
 }
 
 bool HTMLMediaElement::supportsSave() const
 {
     return webMediaPlayer() && webMediaPlayer()->supportsSave();
 }
 
 void HTMLMediaElement::prepareToPlay()

[philipj_slow, 2016/03/11 12:52:41]

This isn't only in preparation to play, but what would be a good name? If you
can't think of one, maybe just setIgnorePreloadNone()?

[Srirama, 2016/03/11 14:58:20]

I will go with setIgnorePreloadNone.

 {
     WTF_LOG(Media, "HTMLMediaElement::prepareToPlay(%p)", this);
-    if (m_havePreparedToPlay)
-        return;
-    m_havePreparedToPlay = true;
-
-    if (loadIsDeferred())
-        startDeferredLoad();
+    m_forceEffectivePreloadAuto = true;
+    setPlayerPreload();
 }
 
 void HTMLMediaElement::seek(double time)
 {
     WTF_LOG(Media, "HTMLMediaElement::seek(%p, %f)", this, time);
 
     // 2 - If the media element's readyState is HAVE_NOTHING, abort these steps.
     if (m_readyState == HAVE_NOTHING)
         return;
 
@@ skipping 308 matching lines @@
     // https://www.w3.org/Bugs/Public/show_bug.cgi?id=28950
 
     // TODO(philipj): Try to make "metadata" the default preload state:
     // https://crbug.com/310450
     UseCounter::count(document(), UseCounter::HTMLMediaElementPreloadDefault);
     return WebMediaPlayer::PreloadAuto;
 }
 
 WebMediaPlayer::Preload HTMLMediaElement::effectivePreloadType() const
 {
-    return autoplay() ? WebMediaPlayer::PreloadAuto : preloadType();
+    if (autoplay())
+        return WebMediaPlayer::PreloadAuto;
+
+    WebMediaPlayer::Preload preload = preloadType();
+    if (m_forceEffectivePreloadAuto && preload == WebMediaPlayer::PreloadNone)

[philipj_slow, 2016/03/11 12:52:41]

Looking at https://www.w3.org/Bugs/Public/show_bug.cgi?id=28921#c3 again, I see
that this isn't quite what Firefox does.

If this instead returns WebMediaPlayer::PreloadMetaData to match Firefox, a very
explicit name would be m_clampEffectivePreloadToMetadataOrHigher, but maybe
m_ignorePreloadNone would be an OK name.

As for the difference, if the distinction is actually made in
WebMediaPlayerImpl, it would be in the amount of data that is buffered after
seeking. Either as little as possible (metadata) or as much as possible (auto).
Might be worth testing manually, but it's a hard to write a fast and reliable
test for this kind of thing. Maybe att effectivePreload to Internals.idl to test
this?

[Srirama, 2016/03/11 14:58:20]

You mean *"Maybe add effectivePreload"? I will try adding it to internals.idl
and write a test.

[philipj_slow, 2016/03/11 18:57:37]

Yes, right. The tests could simply verify that load(), play() and setting
currentTime forces the effective preload state to metadata if it was none.

+        return WebMediaPlayer::PreloadAuto;
+
+    return preload;
 }
 
 ScriptPromise HTMLMediaElement::playForBindings(ScriptState* scriptState)
 {
     Nullable<ExceptionCode> code = play();
     if (!code.isNull()) {
         String message;
         switch (code.get()) {
         case NotAllowedError:
             message = "play() can only be initiated by a user gesture.";
@@ skipping 50 matching lines @@
 {
     WTF_LOG(Media, "HTMLMediaElement::playInternal(%p)", this);
 
     // Always return the buffering strategy to normal when not paused,
     // regardless of the cause. (In contrast with aggressive buffering which is
     // only enabled by pause(), not pauseInternal().)
     if (webMediaPlayer())
         webMediaPlayer()->setBufferingStrategy(WebMediaPlayer::BufferingStrategy::Normal);
 
     // 4.8.10.9. Playing the media resource
-    if (m_networkState == NETWORK_EMPTY)
-        scheduleDelayedAction(LoadMediaResource);
+    if (m_networkState == NETWORK_EMPTY) {
+        // TODO(srirama.m): Remove scheduleNextSourceChild() here and
+        // post a micro task inside invokeResourceSelectionAlgorithm().
+        // See http://crbug.com/593289 for more details.
+        invokeResourceSelectionAlgorithm();
+        scheduleNextSourceChild();
+    }
 
     // Generally "ended" and "looping" are exclusive. Here, the loop attribute
     // is ignored to seek back to start in case loop was set after playback
     // ended. See http://crbug.com/364442
     if (endedPlayback(LoopCondition::Ignored))
         seek(0);
 
     if (m_paused) {
         m_paused = false;
         invalidateCachedTime();
@@ skipping 41 matching lines @@
     if (webMediaPlayer() && UserGestureIndicator::processingUserGesture())
         webMediaPlayer()->setBufferingStrategy(WebMediaPlayer::BufferingStrategy::Aggressive);
 
     pauseInternal();
 }
 
 void HTMLMediaElement::pauseInternal()
 {
     WTF_LOG(Media, "HTMLMediaElement::pauseInternal(%p)", this);
 
-    if (m_networkState == NETWORK_EMPTY)
-        scheduleDelayedAction(LoadMediaResource);
+    if (m_networkState == NETWORK_EMPTY) {
+        // TODO(srirama.m): Remove scheduleNextSourceChild() here and
+        // post a micro task inside invokeResourceSelectionAlgorithm().
+        // See http://crbug.com/593289 for more details.
+        invokeResourceSelectionAlgorithm();
+        scheduleNextSourceChild();
+    }
 
     m_autoplayHelper.pauseMethodCalled();
 
     m_autoplaying = false;
 
     if (!m_paused) {
         recordMetricsIfPausing();
 
         m_paused = true;
         scheduleTimeupdateEvent(false);
@@ skipping 315 matching lines @@
     // 5. Populate the new text track's list of cues with the cues parsed so far, folllowing the guidelines for exposing
     // cues, and begin updating it dynamically as necessary.
     //   - Thess are all done by the media engine.
 
     // 6. Set the new text track's readiness state to loaded.
     textTrack->setReadinessState(TextTrack::Loaded);
 
     // 7. Set the new text track's mode to the mode consistent with the user's preferences and the requirements of
     // the relevant specification for the data.
     //  - This will happen in honorUserPreferencesForAutomaticTextTrackSelection()
-    scheduleDelayedAction(LoadTextTrackResource);
+    scheduleTextTrackResourceLoad();
 
     // 8. Add the new text track to the media element's list of text tracks.
     // 9. Fire an event with the name addtrack, that does not bubble and is not cancelable, and that uses the TrackEvent
     // interface, with the track attribute initialized to the text track's TextTrack object, at the media element's
     // textTracks attribute's TextTrackList object.
     addTextTrack(textTrack);
 }
 
 void HTMLMediaElement::removeTextTrack(WebInbandTextTrack* webTrack)
 {
@@ skipping 99 matching lines @@
     // media element's list of text tracks ... [continues in TextTrackList::append]
     TextTrack* textTrack = trackElement->track();
     if (!textTrack)
         return;
 
     addTextTrack(textTrack);
 
     // Do not schedule the track loading until parsing finishes so we don't start before all tracks
     // in the markup have been added.
     if (isFinishedParsingChildren())
-        scheduleDelayedAction(LoadTextTrackResource);
+        scheduleTextTrackResourceLoad();
 }
 
 void HTMLMediaElement::didRemoveTrackElement(HTMLTrackElement* trackElement)
 {
 #if !LOG_DISABLED
     KURL url = trackElement->getNonEmptyURLAttribute(srcAttr);
     WTF_LOG(Media, "HTMLMediaElement::didRemoveTrackElement(%p) - 'src' is %s", this, urlForLoggingMedia(url).utf8().data());
 #endif
 
     TextTrack* textTrack = trackElement->track();
@@ skipping 164 matching lines @@
 #endif
 
     // We should only consider a <source> element when there is not src attribute at all.
     if (fastHasAttribute(srcAttr))
         return;
 
     // 4.8.8 - If a source element is inserted as a child of a media element that has no src
     // attribute and whose networkState has the value NETWORK_EMPTY, the user agent must invoke
     // the media element's resource selection algorithm.
     if (getNetworkState() == HTMLMediaElement::NETWORK_EMPTY) {
-        scheduleDelayedAction(LoadMediaResource);
+        // TODO(srirama.m): Remove scheduleNextSourceChild() here and
+        // post a micro task inside invokeResourceSelectionAlgorithm().
+        // See http://crbug.com/593289 for more details.
+        invokeResourceSelectionAlgorithm();
+        scheduleNextSourceChild();
+        // Ignore current |m_nextChildNodeToConsider| and consider |source|.
         m_nextChildNodeToConsider = source;
         return;
     }
 
     if (m_currentSourceNode && source == m_currentSourceNode->nextSibling()) {
         WTF_LOG(Media, "HTMLMediaElement::sourceWasAdded(%p) - <source> inserted immediately after current source", this);
+        // Ignore current |m_nextChildNodeToConsider| and consider |source|.
         m_nextChildNodeToConsider = source;
         return;
     }
 
+    // Consider current |m_nextChildNodeToConsider| as it is already in the middle of processing.
     if (m_nextChildNodeToConsider)
         return;
 
     if (m_loadState != WaitingForSource)
         return;
 
     // 4.8.9.5, resource selection algorithm, source elements section:
     // 21. Wait until the node after pointer is a node other than the end of the list. (This step might wait forever.)
     // 22. Asynchronously await a stable state...
     // 23. Set the element's delaying-the-load-event flag back to true (this delays the load event again, in case
@@ skipping 364 matching lines @@
 void HTMLMediaElement::stop()
 {
     WTF_LOG(Media, "HTMLMediaElement::stop(%p)", this);
 
     recordMetricsIfPausing();
 
     // Close the async event queue so that no events are enqueued.
     cancelPendingEventsAndCallbacks();
     m_asyncEventQueue->close();
 
-    // Stop the playback without generating events
+    // Clear everything in the Media Element
     clearMediaPlayer(-1);
     m_readyState = HAVE_NOTHING;
     m_readyStateMaximum = HAVE_NOTHING;
     setNetworkState(NETWORK_EMPTY);
     setShouldDelayLoadEvent(false);
     m_currentSourceNode = nullptr;
     invalidateCachedTime();
     cueTimeline().updateActiveCues(0);
     m_playing = false;
     m_paused = true;
@@ skipping 351 matching lines @@
 }
 
 void* HTMLMediaElement::preDispatchEventHandler(Event* event)
 {
     if (event && event->type() == EventTypeNames::webkitfullscreenchange)
         configureMediaControls();
 
     return nullptr;
 }
 
-// TODO(srirama.m): Refactor this and clearMediaPlayer to the extent possible.
+// TODO(srirama.m): Merge it to resetMediaElement if possible and remove it.
 void HTMLMediaElement::resetMediaPlayerAndMediaSource()
 {
     closeMediaSource();
 
     {
         AudioSourceProviderClientLockScope scope(*this);
         clearMediaPlayerAndAudioSourceProviderClientWithoutLocking();
     }
 
     // We haven't yet found out if any remote routes are available.
@@ skipping 283 matching lines @@
 {
     visitor->trace(m_client);
 }
 
 DEFINE_TRACE(HTMLMediaElement::AudioSourceProviderImpl)
 {
     visitor->trace(m_client);
 }
 
 } // namespace blink