Bug 1360334 - Improve error handling. r=padenot

MozReview-Commit-ID: 5tIXzzisg0V

--HG--
extra : source : 0dc85355af3d166038ccf6e0fd161bd614b0ead2

dom/media/GraphDriver.cpp

@@ -35,7 +35,8 @@ GraphDriver::GraphDriver(MediaStreamGraphImpl* aGraphImpl)
     mWaitState(WAITSTATE_RUNNING),
     mCurrentTimeStamp(TimeStamp::Now()),
     mPreviousDriver(nullptr),
-    mNextDriver(nullptr)
+    mNextDriver(nullptr),
+    mScheduled(false)
 { }
 
 void GraphDriver::SetGraphTime(GraphDriver* aPreviousDriver,
@@ -135,6 +136,12 @@ void GraphDriver::SetPreviousDriver(GraphDriver* aPreviousDriver)
   mPreviousDriver = aPreviousDriver;
 }
 
+bool GraphDriver::Scheduled()
+{
+  GraphImpl()->GetMonitor().AssertCurrentThreadOwns();
+  return mScheduled;
+}
+
 ThreadedDriver::ThreadedDriver(MediaStreamGraphImpl* aGraphImpl)
   : GraphDriver(aGraphImpl)
 { }
@@ -181,7 +188,7 @@ public:
     LOG(LogLevel::Debug,
         ("Starting a new system driver for graph %p", mDriver->mGraphImpl));
 
-    GraphDriver* previousDriver = nullptr;
+    RefPtr<GraphDriver> previousDriver;
     {
       MonitorAutoLock mon(mDriver->mGraphImpl->GetMonitor());
       previousDriver = mDriver->PreviousDriver();
@@ -190,7 +197,7 @@ public:
       LOG(LogLevel::Debug,
           ("%p releasing an AudioCallbackDriver(%p), for graph %p",
            mDriver.get(),
-           previousDriver,
+           previousDriver.get(),
            mDriver->GraphImpl()));
       MOZ_ASSERT(!mDriver->AsAudioCallbackDriver());
       RefPtr<AsyncCubebTask> releaseEvent =
@@ -224,7 +231,8 @@ ThreadedDriver::Start()
     // Note: mThread may be null during event->Run() if we pass to NewNamedThread!  See AudioInitTask
     nsresult rv = NS_NewNamedThread("MediaStreamGrph", getter_AddRefs(mThread));
     if (NS_SUCCEEDED(rv)) {
-      mThread->EventTarget()->Dispatch(event.forget(), NS_DISPATCH_NORMAL);
+      rv = mThread->EventTarget()->Dispatch(event.forget(), NS_DISPATCH_NORMAL);
+      mScheduled = NS_SUCCEEDED(rv);
     }
   }
 }
@@ -796,7 +804,8 @@ AudioCallbackDriver::Start()
        "to ensure it runs after previous shutdown."));
   RefPtr<AsyncCubebTask> initEvent =
     new AsyncCubebTask(AsAudioCallbackDriver(), AsyncCubebOperation::INIT);
-  initEvent->Dispatch();
+  nsresult rv = initEvent->Dispatch();
+  mScheduled = NS_SUCCEEDED(rv);
 }
 
 bool
@@ -1069,13 +1078,25 @@ void
 AudioCallbackDriver::StateCallback(cubeb_state aState)
 {
   LOG(LogLevel::Debug, ("AudioCallbackDriver State: %d", aState));
-  // If we don't have an audio stream here, this means that the stream
-  // initialization has failed. A fallback on a SystemCallDriver will happen at
-  // the callsite of `cubeb_stream_init`.
-  if (aState == CUBEB_STATE_ERROR && mAudioStream) {
+
+  if (aState == CUBEB_STATE_ERROR) {
+    if (!mAudioStream) {
+      // If we don't have an audio stream here, this means that the stream
+      // initialization has failed. A fallback on a SystemCallDriver will happen at
+      // the callsite of `cubeb_stream_init`.
+      return;
+    }
+
+    MonitorAutoLock lock(GraphImpl()->GetMonitor());
+
+    if (NextDriver() && NextDriver()->Scheduled()) {
+      // We are switching to another driver that has already been scheduled
+      // to be initialized and started. There's nothing for us to do here.
+      return;
+    }
+
     // Fall back to a driver using a normal thread. If needed,
     // the graph will try to re-open an audio stream later.
-    MonitorAutoLock lock(GraphImpl()->GetMonitor());
     SystemClockDriver* nextDriver = new SystemClockDriver(GraphImpl());
     SetNextDriver(nextDriver);
     RemoveCallback();

dom/media/GraphDriver.h

@@ -150,6 +150,9 @@ public:
   void SetNextDriver(GraphDriver* aNextDriver);
   void SetPreviousDriver(GraphDriver* aPreviousDriver);
 
+  /* Return whether we have been scheduled to start. */
+  bool Scheduled();
+
   /**
    * If we are running a real time graph, get the current time stamp to schedule
    * video frames. This has to be reimplemented by real time drivers.
@@ -253,6 +256,9 @@ protected:
   // driver at the end of this iteration.
   // This must be accessed using the {Set,Get}NextDriver methods.
   RefPtr<GraphDriver> mNextDriver;
+  // This is initially false, but set to true as soon the driver has been
+  // scheduled to start through GraphDriver::Start().
+  bool mScheduled;
   virtual ~GraphDriver()
   { }
 };