Bug 1577537 - Catch AppendMessage calls that could be too late. r=karlt

If all streams and all ports have been destroyed, there's no guarantee that the
graph is still alive. By forbidding AppendMessage calls after this point, we can
catch bugs with the offending callsite still being in the stack.

Differential Revision: https://phabricator.services.mozilla.com/D44223

--HG--
extra : moz-landing-system : lando

dom/media/MediaStreamGraph.cpp

@@ -1793,8 +1793,8 @@ void MediaStreamGraphImpl::SignalMainThreadCleanup() {
 
 void MediaStreamGraphImpl::AppendMessage(UniquePtr<ControlMessage> aMessage) {
   MOZ_ASSERT(NS_IsMainThread(), "main thread only");
-  MOZ_ASSERT(!aMessage->GetStream() || !aMessage->GetStream()->IsDestroyed(),
-             "Stream already destroyed");
+  MOZ_ASSERT_IF(aMessage->GetStream(), !aMessage->GetStream()->IsDestroyed());
+  MOZ_DIAGNOSTIC_ASSERT(mMainThreadStreamCount > 0 || mMainThreadPortCount > 0);
 
   if (mDetectedNotRunning &&
       LifecycleStateRef() > LIFECYCLE_WAITING_FOR_MAIN_THREAD_CLEANUP) {
@@ -2001,8 +2001,11 @@ void MediaStream::Destroy() {
     }
     void RunDuringShutdown() override { Run(); }
   };
-  GraphImpl()->RemoveStream(this);
-  GraphImpl()->AppendMessage(MakeUnique<Message>(this));
+  // Keep a reference to the graph, since Message might RunDuringShutdown()
+  // synchronously and make GraphImpl() invalid.
+  RefPtr<MediaStreamGraphImpl> graph = GraphImpl();
+  graph->AppendMessage(MakeUnique<Message>(this));
+  graph->RemoveStream(this);
   // Message::RunDuringShutdown may have removed this stream from the graph,
   // but our kungFuDeathGrip above will have kept this stream alive if
   // necessary.
@@ -2984,7 +2987,11 @@ void MediaInputPort::Destroy() {
     void RunDuringShutdown() override { Run(); }
     MediaInputPort* mPort;
   };
-  GraphImpl()->AppendMessage(MakeUnique<Message>(this));
+  // Keep a reference to the graph, since Message might RunDuringShutdown()
+  // synchronously and make GraphImpl() invalid.
+  RefPtr<MediaStreamGraphImpl> graph = GraphImpl();
+  graph->AppendMessage(MakeUnique<Message>(this));
+  --graph->mMainThreadPortCount;
 }
 
 MediaStreamGraphImpl* MediaInputPort::GraphImpl() { return mGraph; }
@@ -3102,6 +3109,7 @@ already_AddRefed<MediaInputPort> ProcessedMediaStream::AllocateInputPort(
     }
   }
   port->SetGraphImpl(GraphImpl());
+  ++GraphImpl()->mMainThreadPortCount;
   GraphImpl()->AppendMessage(MakeUnique<Message>(port));
   return port.forget();
 }

dom/media/MediaStreamGraphImpl.h

@@ -662,6 +662,15 @@ class MediaStreamGraphImpl : public MediaStreamGraph,
    */
   size_t mMainThreadStreamCount = 0;
 
+  /**
+   * Main-thread view of the number of ports in this graph, to catch bugs.
+   *
+   * When this becomes zero, and mMainThreadStreamCount is 0, the graph is
+   * marked as forbidden to add more ControlMessages to. It will be shut down
+   * shortly after.
+   */
+  size_t mMainThreadPortCount = 0;
+
   /**
    * Graphs own owning references to their driver, until shutdown. When a driver
    * switch occur, previous driver is either deleted, or it's ownership is