b=923301 add MediaStreamGraph::RunAfterPendingUpdates() r=roc

--HG--
extra : transplant_source : %89%21%AE%87%C7%9C%07%28%3D%60T%83%16n%DC%C9O%87iy

content/media/MediaStreamGraph.cpp

@@ -1919,6 +1919,40 @@ MediaStream::RemoveListener(MediaStreamListener* aListener)
   }
 }
 
+void
+MediaStream::RunAfterPendingUpdates(nsRefPtr<nsIRunnable> aRunnable)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  MediaStreamGraphImpl* graph = GraphImpl();
+
+  // Special case when a non-realtime graph has not started, to ensure the
+  // runnable will run in finite time.
+  if (!(graph->mRealtime || graph->mNonRealtimeProcessing)) {
+    aRunnable->Run();
+  }
+
+  class Message : public ControlMessage {
+  public:
+    explicit Message(MediaStream* aStream,
+                     already_AddRefed<nsIRunnable> aRunnable)
+      : ControlMessage(aStream)
+      , mRunnable(aRunnable) {}
+    virtual void Run() MOZ_OVERRIDE
+    {
+      mStream->Graph()->
+        DispatchToMainThreadAfterStreamStateUpdate(mRunnable.forget());
+    }
+    virtual void RunDuringShutdown() MOZ_OVERRIDE
+    {
+      mRunnable->Run();
+    }
+  private:
+    nsRefPtr<nsIRunnable> mRunnable;
+  };
+
+  graph->AppendMessage(new Message(this, aRunnable.forget()));
+}
+
 void
 MediaStream::SetTrackEnabledImpl(TrackID aTrackID, bool aEnabled)
 {

content/media/MediaStreamGraph.h

@@ -346,6 +346,20 @@ public:
     NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
     mMainThreadListeners.RemoveElement(aListener);
   }
+  /**
+   * Ensure a runnable will run on the main thread after running all pending
+   * updates that were sent from the graph thread or will be sent before the
+   * graph thread receives the next graph update.
+   *
+   * If the graph has been shutdown or destroyed, or if it is non-realtime
+   * and has not started, then the runnable will be run
+   * synchronously/immediately.  (There are no pending updates in these
+   * situations.)
+   *
+   * Main thread only.
+   */
+  void RunAfterPendingUpdates(nsRefPtr<nsIRunnable> aRunnable);
+
   // Signal that the client is done with this MediaStream. It will be deleted later.
   virtual void Destroy();
   // Returns the main-thread's view of how much data has been processed by

content/media/MediaStreamGraphImpl.h

@@ -72,11 +72,11 @@ struct StreamUpdate {
 
 /**
  * This represents a message passed from the main thread to the graph thread.
- * A ControlMessage always references a particular affected stream.
+ * A ControlMessage always has a weak reference a particular affected stream.
  */
 class ControlMessage {
 public:
-  ControlMessage(MediaStream* aStream) : mStream(aStream)
+  explicit ControlMessage(MediaStream* aStream) : mStream(aStream)
   {
     MOZ_COUNT_CTOR(ControlMessage);
   }