Have HTMLMediaElement::play() return a Promise.

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 efeaceaddd63eecdb4b7d2f1a3ec83db944fcc60..34ceb68304e357d06e9e40f2a9c27a76aa56ab07 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -29,11 +29,11 @@
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
 #include "bindings/core/v8/ScriptController.h"
 #include "bindings/core/v8/ScriptEventListener.h"
+#include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/HTMLNames.h"
 #include "core/css/MediaList.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/ElementTraversal.h"
-#include "core/dom/ExceptionCode.h"
 #include "core/dom/Fullscreen.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/Event.h"
@@ -72,6 +72,8 @@
 #include "platform/MIMETypeFromURL.h"
 #include "platform/MIMETypeRegistry.h"
 #include "platform/RuntimeEnabledFeatures.h"
+#include "platform/Task.h"
+#include "platform/ThreadSafeFunctional.h"
 #include "platform/UserGestureIndicator.h"
 #include "platform/audio/AudioBus.h"
 #include "platform/audio/AudioSourceProviderClient.h"
@@ -730,6 +732,8 @@ void HTMLMediaElement::prepareForLoad()
     // one of the task queues, then remove those tasks.
     cancelPendingEventsAndCallbacks();
 
+    rejectPlayPromises(AbortError, "The play() request was interrupted by a new load request.");
+
     // 3 - If the media element's networkState is set to NETWORK_LOADING or NETWORK_IDLE, queue
     // a task to fire a simple event named abort at the media element.
     if (m_networkState == NETWORK_LOADING || m_networkState == NETWORK_IDLE)
@@ -1244,33 +1248,33 @@ void HTMLMediaElement::noneSupported()
     m_loadState = WaitingForSource;
     m_currentSourceNode = nullptr;
 
-    // 4.8.10.5
-    // 6 - Reaching this step indicates that the media resource failed to load or that the given
-    // URL could not be resolved. In one atomic operation, run the following steps:
+    // 4.8.13.5
+    // The dedicated media source failure steps are the following steps:
 
-    // 6.1 - Set the error attribute to a new MediaError object whose code attribute is set to
+    // 1 - Set the error attribute to a new MediaError object whose code attribute is set to
     // MEDIA_ERR_SRC_NOT_SUPPORTED.
     m_error = MediaError::create(MediaError::MEDIA_ERR_SRC_NOT_SUPPORTED);
 
-    // 6.2 - Forget the media element's media-resource-specific text tracks.
+    // 2 - Forget the media element's media-resource-specific text tracks.
     forgetResourceSpecificTracks();
 
-    // 6.3 - Set the element's networkState attribute to the NETWORK_NO_SOURCE value.
+    // 3 - Set the element's networkState attribute to the NETWORK_NO_SOURCE value.
     setNetworkState(NETWORK_NO_SOURCE);
 
-    // 7 - Queue a task to fire a simple event named error at the media element.
+    // 4 - Set the element's show poster flag to true.
+    updateDisplayState();
+
+    // 5 - Fire a simple event named error at the media element.
     scheduleEvent(EventTypeNames::error);
 
+    // 6 - Reject pending play promises with NotSupportedError.
+    scheduleRejectPlayPromises(NotSupportedError, "Failed to load because no supported source was found.");
+
     closeMediaSource();
 
-    // 8 - Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
+    // 7 - Set the element's delaying-the-load-event flag to false. This stops delaying the load event.
     setShouldDelayLoadEvent(false);
 
-    // 9 - Abort these steps. Until the load() method is invoked or the src attribute is changed,
-    // the element won't attempt to load another resource.
-
-    updateDisplayState();
-
     if (layoutObject())
         layoutObject()->updateFromElement();
 }
@@ -1519,7 +1523,7 @@ void HTMLMediaElement::setReadyState(ReadyState state)
     if (m_readyState == HAVE_FUTURE_DATA && oldState <= HAVE_CURRENT_DATA && tracksAreReady) {
         scheduleEvent(EventTypeNames::canplay);
         if (isPotentiallyPlaying)
-            scheduleEvent(EventTypeNames::playing);
+            scheduleNotifyPlaying();
         shouldUpdateDisplayState = true;
     }
 
@@ -1527,7 +1531,7 @@ void HTMLMediaElement::setReadyState(ReadyState state)
         if (oldState <= HAVE_CURRENT_DATA) {
             scheduleEvent(EventTypeNames::canplay);
             if (isPotentiallyPlaying)
-                scheduleEvent(EventTypeNames::playing);
+                scheduleNotifyPlaying();
         }
 
         // Check for autoplay, and record metrics about it if needed.
@@ -1540,7 +1544,7 @@ void HTMLMediaElement::setReadyState(ReadyState state)
                 m_paused = false;
                 invalidateCachedTime();
                 scheduleEvent(EventTypeNames::play);
-                scheduleEvent(EventTypeNames::playing);
+                scheduleNotifyPlaying();
                 m_autoplaying = false;
             }
         }
@@ -1932,7 +1936,32 @@ WebMediaPlayer::Preload HTMLMediaElement::effectivePreloadType() const
     return autoplay() ? WebMediaPlayer::PreloadAuto : preloadType();
 }
 
-void HTMLMediaElement::play()
+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.";
+            break;
+        case NotSupportedError:
+            message = "The element has no supported sources.";
+            break;
+        default:
+            ASSERT_NOT_REACHED();
+        }
+        return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(code.get(), message));
+    }
+
+    ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
+    ScriptPromise promise = resolver->promise();
+
+    m_playResolvers.append(resolver);
+    return promise;
+}
+
+Nullable<ExceptionCode> HTMLMediaElement::play()
 {
     WTF_LOG(Media, "HTMLMediaElement::play(%p)", this);
 
@@ -1945,7 +1974,7 @@ void HTMLMediaElement::play()
             recordAutoplayMetric(PlayMethodFailed);
             String message = ExceptionMessages::failedToExecute("play", "HTMLMediaElement", "API can only be initiated by a user gesture.");
             document().addConsoleMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel, message));
-            return;
+            return NotAllowedError;
         }
     } else if (m_userGestureRequiredForPlay) {
         if (m_autoplayMediaCounted)
@@ -1953,7 +1982,12 @@ void HTMLMediaElement::play()
         m_userGestureRequiredForPlay = false;
     }
 
+    if (m_error && m_error->code() == MediaError::MEDIA_ERR_SRC_NOT_SUPPORTED)
+        return NotSupportedError;
+
     playInternal();
+
+    return nullptr;
 }
 
 void HTMLMediaElement::playInternal()
@@ -1984,8 +2018,11 @@ void HTMLMediaElement::playInternal()
         if (m_readyState <= HAVE_CURRENT_DATA)
             scheduleEvent(EventTypeNames::waiting);
         else if (m_readyState >= HAVE_FUTURE_DATA)
-            scheduleEvent(EventTypeNames::playing);
+            scheduleNotifyPlaying();
+    } else if (m_readyState >= HAVE_FUTURE_DATA) {
+        scheduleResolvePlayPromises();
     }
+
     m_autoplaying = false;
 
     updatePlayState();
@@ -2040,6 +2077,7 @@ void HTMLMediaElement::pauseInternal()
         m_paused = true;
         scheduleTimeupdateEvent(false);
         scheduleEvent(EventTypeNames::pause);
+        scheduleRejectPlayPromises(AbortError, "The play() request was interrupted by a call to pause().");
     }
 
     updatePlayState();
@@ -3494,6 +3532,7 @@ DEFINE_TRACE(HTMLMediaElement)
     visitor->trace(m_cueTimeline);
     visitor->trace(m_textTracks);
     visitor->trace(m_textTracksWhenResourceSelectionBegan);
+    visitor->trace(m_playResolvers);
     visitor->trace(m_audioSourceProvider);
     visitor->template registerWeakMembers<HTMLMediaElement, &HTMLMediaElement::clearWeakMembers>(this);
     visitor->trace(m_autoplayHelper);
@@ -3571,6 +3610,42 @@ void HTMLMediaElement::triggerAutoplayViewportCheckForTesting()
     m_autoplayHelper.triggerAutoplayViewportCheckForTesting();
 }
 
+void HTMLMediaElement::scheduleResolvePlayPromises()
+{
+    Platform::current()->currentThread()->taskRunner()->postTask(
+        BLINK_FROM_HERE, new Task(threadSafeBind(&HTMLMediaElement::resolvePlayPromises, AllowCrossThreadAccess(this))));

[hiroshige, 2016/02/18 18:32:41]

(1) The code seems single threaded, because scheduleResolvePlayPromises() post a
task to the current thread (==main thread?), right?
If so, then we can (or should) use bind() instead of threadSafeBind() here.

(2)
[A] Do we want to keep |*this| alive until the posted task is executed?
or
[B] Do we allow |*this| to be deleted before the task is executed and in that
case just omit the task execution?

In case of [A]:
Basically, bind() does NOT keep a reference if we pass raw pointers (T*) if T is
NOT on Oilpan heap, and DOES keep a reference if T IS on-heap (i.e.
GarbageCollected etc.).
So we have to pass a reference explicitly, perhaps
PassRefPtrWillBeRawPtr<HTMLMediaElement>(this) or something.

In case of [B]:
We have to use weak pointers.
Perhaps WeakPtrWillBeWeakPersistent<HTMLMediaElement>?
But WTF::Function doesn't have sufficient support for passing WeakPersistent.
I'll create a CL for adding this support.

[mlamouri (slow - plz ping), 2016/02/18 19:24:42]

You are correct, it doesn't need to be thread safe but haraken@ told me that it
might be the solution in order to keep the object around. I was probably not
clear when I explained my issue. Glad to hear there is a better solution :)
I think keeping the object alive is fine, it sounds more consistent and probably
will avoid leaking or GC behaviour.

I've applied solution A. PTAL.

+}
+
+void HTMLMediaElement::scheduleRejectPlayPromises(ExceptionCode code, const String& message)
+{
+    Platform::current()->currentThread()->taskRunner()->postTask(
+        BLINK_FROM_HERE, new Task(threadSafeBind(&HTMLMediaElement::rejectPlayPromises, AllowCrossThreadAccess(this), code, message)));
+}
+
+void HTMLMediaElement::scheduleNotifyPlaying()
+{
+    scheduleEvent(EventTypeNames::playing);
+    scheduleResolvePlayPromises();
+}
+
+void HTMLMediaElement::resolvePlayPromises()
+{
+    for (auto& resolver: m_playResolvers)
+        resolver->resolve();
+
+    m_playResolvers.clear();
+}
+
+void HTMLMediaElement::rejectPlayPromises(ExceptionCode code, const String& message)
+{
+    ASSERT(code == AbortError || code == NotSupportedError);
+
+    for (auto& resolver: m_playResolvers)
+        resolver->reject(DOMException::create(code, message));
+
+    m_playResolvers.clear();
+}
+
 void HTMLMediaElement::clearWeakMembers(Visitor* visitor)
 {
     if (!Heap::isHeapObjectAlive(m_audioSourceNode))