Bug 779721. Part 6: Add a flag to track whether the main thread has called Destroy on a stream, and check that flag when sending a message to it. r=jesup

content/media/MediaStreamGraph.cpp

@@ -99,11 +99,12 @@ public:
   // When we're shutting down the application, most messages are ignored but
   // some cleanup messages should still be processed (on the main thread).
   virtual void RunDuringShutdown() {}
+  MediaStream* GetStream() { return mStream; }
 
 protected:
-  // We do not hold a reference to mStream. The main thread will be holding
-  // a reference to the stream while this message is in flight. The last message
-  // referencing a stream is the Destroy message for that stream.
+  // We do not hold a reference to mStream. The graph will be holding
+  // a reference to the stream until the Destroy message is processed. The
+  // last message referencing a stream is the Destroy message for that stream.
   MediaStream* mStream;
 };
 
@@ -1537,6 +1538,9 @@ void
 MediaStreamGraphImpl::AppendMessage(ControlMessage* aMessage)
 {
   NS_ASSERTION(NS_IsMainThread(), "main thread only");
+  NS_ASSERTION(!aMessage->GetStream() ||
+               !aMessage->GetStream()->IsDestroyed(),
+               "Stream already destroyed");
 
   if (mDetectedNotRunning &&
       mLifecycleState > LIFECYCLE_WAITING_FOR_MAIN_THREAD_CLEANUP) {
@@ -1599,6 +1603,7 @@ MediaStream::Destroy()
   };
   mWrapper = nullptr;
   GraphImpl()->AppendMessage(new Message(this));
+  mMainThreadDestroyed = true;
 }
 
 void

content/media/MediaStreamGraph.h

@@ -238,6 +238,7 @@ public:
     , mWrapper(aWrapper)
     , mMainThreadCurrentTime(0)
     , mMainThreadFinished(false)
+    , mMainThreadDestroyed(false)
   {
     for (PRUint32 i = 0; i < ArrayLength(mFirstActiveTracks); ++i) {
       mFirstActiveTracks[i] = TRACK_NONE;
@@ -275,9 +276,22 @@ public:
   void Destroy();
   // Returns the main-thread's view of how much data has been processed by
   // this stream.
-  StreamTime GetCurrentTime() { return mMainThreadCurrentTime; }
+  StreamTime GetCurrentTime()
+  {
+    NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
+    return mMainThreadCurrentTime;
+  }
   // Return the main thread's view of whether this stream has finished.
-  bool IsFinished() { return mMainThreadFinished; }
+  bool IsFinished()
+  {
+    NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
+    return mMainThreadFinished;
+  }
+  bool IsDestroyed()
+  {
+    NS_ASSERTION(NS_IsMainThread(), "Call only on main thread");
+    return mMainThreadDestroyed;
+  }
 
   friend class MediaStreamGraphImpl;
 
@@ -400,6 +414,7 @@ protected:
   // Main-thread views of state
   StreamTime mMainThreadCurrentTime;
   bool mMainThreadFinished;
+  bool mMainThreadDestroyed;
 };
 
 /**