Bug 759908. Create MediaStreamListener::NotifyConsumptionChanged. r=jesup

--HG--
extra : rebase_source : f9479b836ec92170782eb01ea8b97004b057ceb7

content/media/MediaStreamGraph.cpp

@@ -205,6 +205,11 @@ public:
    * will take effect.
    */
   void ChooseActionTime();
+  /**
+   * Update the consumption state of aStream to reflect whether its data
+   * is needed or not.
+   */
+  void UpdateConsumptionState(SourceMediaStream* aStream);
   /**
    * Extract any state updates pending in aStream, and apply them.
    */
@@ -612,6 +617,22 @@ MediaStreamGraphImpl::ChooseActionTime()
   mLastActionTime = GetEarliestActionTime();
 }
 
+void
+MediaStreamGraphImpl::UpdateConsumptionState(SourceMediaStream* aStream)
+{
+  bool isConsumed = !aStream->mAudioOutputs.IsEmpty() ||
+    !aStream->mVideoOutputs.IsEmpty();
+  MediaStreamListener::Consumption state = isConsumed ? MediaStreamListener::CONSUMED
+    : MediaStreamListener::NOT_CONSUMED;
+  if (state != aStream->mLastConsumptionState) {
+    aStream->mLastConsumptionState = state;
+    for (PRUint32 j = 0; j < aStream->mListeners.Length(); ++j) {
+      MediaStreamListener* l = aStream->mListeners[j];
+      l->NotifyConsumptionChanged(this, state);
+    }
+  }
+}
+
 void
 MediaStreamGraphImpl::ExtractPendingInput(SourceMediaStream* aStream)
 {
@@ -1267,6 +1288,7 @@ MediaStreamGraphImpl::RunThread()
     for (PRUint32 i = 0; i < mStreams.Length(); ++i) {
       SourceMediaStream* is = mStreams[i]->AsSourceStream();
       if (is) {
+        UpdateConsumptionState(is);
         ExtractPendingInput(is);
       }
     }

content/media/MediaStreamGraph.h

@@ -94,12 +94,24 @@ public:
 
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaStreamListener)
 
+  enum Consumption {
+    CONSUMED,
+    NOT_CONSUMED
+  };
+  /**
+   * Notify that the stream is hooked up and we'd like to start or stop receiving
+   * data on it. Only fires on SourceMediaStreams.
+   * The initial state is assumed to be NOT_CONSUMED.
+   */
+  virtual void NotifyConsumptionChanged(MediaStreamGraph* aGraph, Consumption aConsuming) {}
+
   enum Blocking {
     BLOCKED,
     UNBLOCKED
   };
   /**
-   * Notify that the blocking status of the stream changed.
+   * Notify that the blocking status of the stream changed. The initial state
+   * is assumed to be BLOCKED.
    */
   virtual void NotifyBlockingChanged(MediaStreamGraph* aGraph, Blocking aBlocked) {}
 
@@ -371,8 +383,11 @@ protected:
 class SourceMediaStream : public MediaStream {
 public:
   SourceMediaStream(nsDOMMediaStream* aWrapper) :
-    MediaStream(aWrapper), mMutex("mozilla::media::SourceMediaStream"),
-    mUpdateKnownTracksTime(0), mUpdateFinished(false), mDestroyed(false)
+    MediaStream(aWrapper),
+    mLastConsumptionState(MediaStreamListener::NOT_CONSUMED),
+    mMutex("mozilla::media::SourceMediaStream"),
+    mUpdateKnownTracksTime(0),
+    mUpdateFinished(false), mDestroyed(false)
   {}
 
   virtual SourceMediaStream* AsSourceStream() { return this; }
@@ -471,6 +486,9 @@ protected:
     return nsnull;
   }
 
+  // Media stream graph thread only
+  MediaStreamListener::Consumption mLastConsumptionState;
+
   // This must be acquired *before* MediaStreamGraphImpl's lock, if they are
   // held together.
   Mutex mMutex;