Fix race when HTMLMediaElement.play() is called just after pause().

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 426 matching lines @@
     , m_textTracksVisible(false)
     , m_shouldPerformAutomaticTrackSelection(true)
     , m_tracksAreReady(true)
     , m_processingPreferenceChange(false)
     , m_remoteRoutesAvailable(false)
     , m_playingRemotely(false)
     , m_inOverlayFullscreenVideo(false)
     , m_audioTracks(AudioTrackList::create(*this))
     , m_videoTracks(VideoTrackList::create(*this))
     , m_textTracks(nullptr)
-    , m_playPromiseResolveTask(CancellableTaskFactory::create(this, &HTMLMediaElement::resolvePlayPromises))
-    , m_playPromiseRejectTask(CancellableTaskFactory::create(this, &HTMLMediaElement::rejectPlayPromises))
+    , m_playPromiseResolveTask(CancellableTaskFactory::create(this, &HTMLMediaElement::resolveScheduledPlayPromises))
+    , m_playPromiseRejectTask(CancellableTaskFactory::create(this, &HTMLMediaElement::rejectScheduledPlayPromises))
     , m_audioSourceNode(nullptr)
     , m_autoplayHelperClient(AutoplayHelperClientImpl::create(this))
     , m_autoplayHelper(AutoplayExperimentHelper::create(m_autoplayHelperClient.get()))
     , m_remotePlaybackClient(nullptr)
 {
     ThreadState::current()->registerPreFinalizer(this);
 
     DVLOG(MEDIA_LOG_LEVEL) << "HTMLMediaElement(" << (void*)this << ")";
 
     // If any experiment is enabled, then we want to enable a user gesture by
@@ skipping 938 matching lines @@
 
 void HTMLMediaElement::cancelPendingEventsAndCallbacks()
 {
     DVLOG(MEDIA_LOG_LEVEL) << "cancelPendingEventsAndCallbacks(" << (void*)this << ")";
     m_asyncEventQueue->cancelAllEvents();
 
     for (HTMLSourceElement* source = Traversal<HTMLSourceElement>::firstChild(*this); source; source = Traversal<HTMLSourceElement>::nextSibling(*source))
         source->cancelPendingErrorEvent();
 
     m_playPromiseResolveTask->cancel();
+    m_playPromiseResolveList.clear();
     m_playPromiseRejectTask->cancel();
+    m_playPromiseRejectList.clear();
 }
 
 void HTMLMediaElement::networkStateChanged()
 {
     setNetworkState(webMediaPlayer()->getNetworkState());
 }
 
 void HTMLMediaElement::mediaLoadingFailed(WebMediaPlayer::NetworkState error)
 {
     stopPeriodicTimers();
@@ skipping 604 matching lines @@
 
     WebMediaPlayer::Preload preload = preloadType();
     if (m_ignorePreloadNone && preload == WebMediaPlayer::PreloadNone)
         return WebMediaPlayer::PreloadMetaData;
 
     return preload;
 }
 
 ScriptPromise HTMLMediaElement::playForBindings(ScriptState* scriptState)
 {
+    // We have to share the same logic for internal and external callers. The
+    // internal callers do not want to receive a Promise back but when ::play()
+    // is called, |m_playPromiseResolvers| needs to be populated. What this code
+    // does is to populate |m_playPromiseResolvers| before calling ::play() and
+    // remove the Promise if ::play() failed.
+    ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromise promise = resolver->promise();
+    m_playPromiseResolvers.append(resolver);
+
     Nullable<ExceptionCode> code = play();
     if (!code.isNull()) {
+        DCHECK(!m_playPromiseResolvers.isEmpty());
+        m_playPromiseResolvers.removeLast();
+
         String message;
         switch (code.get()) {
         case NotAllowedError:
             message = "play() can only be initiated by a user gesture.";
             break;
         case NotSupportedError:
             message = "The element has no supported sources.";
             break;
         default:
             ASSERT_NOT_REACHED();
         }
-        return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(code.get(), message));
+        resolver->reject(DOMException::create(code.get(), message));
+        return promise;
     }
 
-    ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
-    ScriptPromise promise = resolver->promise();
-
-    m_playResolvers.append(resolver);
     return promise;
 }
 
 Nullable<ExceptionCode> HTMLMediaElement::play()
 {
     DVLOG(MEDIA_LOG_LEVEL) << "play(" << (void*)this << ")";
 
     m_autoplayHelper->playMethodCalled();
 
     if (!UserGestureIndicator::processingUserGesture()) {
@@ skipping 1542 matching lines @@
     visitor->trace(m_asyncEventQueue);
     visitor->trace(m_error);
     visitor->trace(m_currentSourceNode);
     visitor->trace(m_nextChildNodeToConsider);
     visitor->trace(m_mediaSource);
     visitor->trace(m_audioTracks);
     visitor->trace(m_videoTracks);
     visitor->trace(m_cueTimeline);
     visitor->trace(m_textTracks);
     visitor->trace(m_textTracksWhenResourceSelectionBegan);
-    visitor->trace(m_playResolvers);
+    visitor->trace(m_playPromiseResolvers);
+    visitor->trace(m_playPromiseResolveList);
+    visitor->trace(m_playPromiseRejectList);
     visitor->trace(m_audioSourceProvider);
     visitor->trace(m_autoplayHelperClient);
     visitor->trace(m_autoplayHelper);
     visitor->trace(m_srcObject);
     visitor->template registerWeakMembers<HTMLMediaElement, &HTMLMediaElement::clearWeakMembers>(this);
     Supplementable<HTMLMediaElement>::trace(visitor);
     HTMLElement::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
@@ skipping 76 matching lines @@
 // TODO(liberato): remove once autoplay gesture override experiment concludes.
 void HTMLMediaElement::triggerAutoplayViewportCheckForTesting()
 {
     if (FrameView* view = document().view())
         m_autoplayHelper->positionChanged(view->rootFrameToContents(view->computeVisibleArea()));
     m_autoplayHelper->triggerAutoplayViewportCheckForTesting();
 }
 
 void HTMLMediaElement::scheduleResolvePlayPromises()
 {
-    // Per spec, if there are two tasks in the queue, the first task will remove
-    // all the pending promises making the second task useless unless a promise
-    // can be added between the first and second task being run which is not
-    // possible at the moment.
+    // TODO(mlamouri): per spec, we should create a new task but we can't create
+    // a new cancellable task without cancelling the previous one. There are two
+    // approaches then: cancel the previous task and create a new one with the
+    // appended promise list or append the new promise to the current list. The
+    // latter approach is preferred because it might be the less observable
+    // change.
+    DCHECK(m_playPromiseResolveList.isEmpty() || m_playPromiseResolveTask->isPending());
+    if (m_playPromiseResolvers.isEmpty())
+        return;
+
+    m_playPromiseResolveList.appendVector(m_playPromiseResolvers);
+    m_playPromiseResolvers.clear();
+
     if (m_playPromiseResolveTask->isPending())
         return;
 
     Platform::current()->currentThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, m_playPromiseResolveTask->cancelAndCreate());
 }
 
 void HTMLMediaElement::scheduleRejectPlayPromises(ExceptionCode code)
 {
-    // Per spec, if there are two tasks in the queue, the first task will remove
-    // all the pending promises making the second task useless unless a promise
-    // can be added between the first and second task being run which is not
-    // possible at the moment.
+    // TODO(mlamouri): per spec, we should create a new task but we can't create
+    // a new cancellable task without cancelling the previous one. There are two
+    // approaches then: cancel the previous task and create a new one with the
+    // appended promise list or append the new promise to the current list. The
+    // latter approach is preferred because it might be the less observable
+    // change.
+    DCHECK(m_playPromiseRejectList.isEmpty() || m_playPromiseRejectTask->isPending());
+    if (m_playPromiseResolvers.isEmpty())
+        return;
+
+    m_playPromiseRejectList.appendVector(m_playPromiseResolvers);
+    m_playPromiseResolvers.clear();
+
     if (m_playPromiseRejectTask->isPending())
         return;
 
     // TODO(mlamouri): because cancellable tasks can't take parameters, the
     // error code needs to be saved.
     m_playPromiseErrorCode = code;
     Platform::current()->currentThread()->getWebTaskRunner()->postTask(BLINK_FROM_HERE, m_playPromiseRejectTask->cancelAndCreate());
 }
 
 void HTMLMediaElement::scheduleNotifyPlaying()
 {
     scheduleEvent(EventTypeNames::playing);
     scheduleResolvePlayPromises();
 }
 
-void HTMLMediaElement::resolvePlayPromises()
+void HTMLMediaElement::resolveScheduledPlayPromises()
 {
-    for (auto& resolver: m_playResolvers)
+    for (auto& resolver: m_playPromiseResolveList)
         resolver->resolve();
 
-    m_playResolvers.clear();
+    m_playPromiseResolveList.clear();
 }
 
-void HTMLMediaElement::rejectPlayPromises()
+void HTMLMediaElement::rejectScheduledPlayPromises()
 {
     // TODO(mlamouri): the message is generated based on the code because
     // arguments can't be passed to a cancellable task. In order to save space
     // used by the object, the string isn't saved.
-    ASSERT(m_playPromiseErrorCode == AbortError || m_playPromiseErrorCode == NotSupportedError);
+    DCHECK(m_playPromiseErrorCode == AbortError || m_playPromiseErrorCode == NotSupportedError);
     if (m_playPromiseErrorCode == AbortError)
-        rejectPlayPromises(AbortError, "The play() request was interrupted by a call to pause().");
+        rejectPlayPromisesInternal(AbortError, "The play() request was interrupted by a call to pause().");
     else
-        rejectPlayPromises(NotSupportedError, "Failed to load because no supported source was found.");
+        rejectPlayPromisesInternal(NotSupportedError, "Failed to load because no supported source was found.");
 }
 
 void HTMLMediaElement::rejectPlayPromises(ExceptionCode code, const String& message)
 {
-    ASSERT(code == AbortError || code == NotSupportedError);
+    m_playPromiseRejectList.appendVector(m_playPromiseResolvers);
+    m_playPromiseResolvers.clear();
+    rejectPlayPromisesInternal(code, message);
+}
 
-    for (auto& resolver: m_playResolvers)
+void HTMLMediaElement::rejectPlayPromisesInternal(ExceptionCode code, const String& message)
+{
+    DCHECK(code == AbortError || code == NotSupportedError);
+
+    for (auto& resolver: m_playPromiseRejectList)
         resolver->reject(DOMException::create(code, message));
 
-    m_playResolvers.clear();
+    m_playPromiseRejectList.clear();
 }
 
 EnumerationHistogram& HTMLMediaElement::showControlsHistogram() const
 {
     if (isHTMLVideoElement()) {
         DEFINE_STATIC_LOCAL(EnumerationHistogram, histogram, ("Media.Controls.Show.Video", MediaControlsShowMax));
         return histogram;
     }
 
     DEFINE_STATIC_LOCAL(EnumerationHistogram, histogram, ("Media.Controls.Show.Audio", MediaControlsShowMax));
@@ skipping 125 matching lines @@
 
 IntRect HTMLMediaElement::AutoplayHelperClientImpl::absoluteBoundingBoxRect() const
 {
     IntRect result;
     if (LayoutObject* object = m_element->layoutObject())
         result = object->absoluteBoundingBoxRect();
     return result;
 }
 
 } // namespace blink