Bug 1542931 add a mechanism to notify engine on graph thread of forced shutdown r=padenot

This will be used to release the AudioWorkletProcessor on the correct thread.

Depends on D34480

Differential Revision: https://phabricator.services.mozilla.com/D34481

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

dom/media/MediaStreamGraph.cpp

@@ -1347,6 +1347,12 @@ void MediaStreamGraphImpl::Process() {
 
 bool MediaStreamGraphImpl::UpdateMainThreadState() {
   MOZ_ASSERT(OnGraphThread());
+  if (mForceShutDown) {
+    for (MediaStream* stream : AllStreams()) {
+      stream->NotifyForcedShutdown();
+    }
+  }
+
   MonitorAutoLock lock(mMonitor);
   bool finalUpdate =
       mForceShutDown || (IsEmpty() && mBackMessageQueue.IsEmpty());

dom/media/MediaStreamGraph.h

@@ -511,6 +511,10 @@ class MediaStream : public mozilla::LinkedListElement<MediaStream> {
   void DecrementSuspendCount();
 
  protected:
+  // Called on graph thread before handing control to the main thread to
+  // release streams.
+  virtual void NotifyForcedShutdown() {}
+
   // |AdvanceTimeVaryingValuesToCurrentTime| will be override in
   // SourceMediaStream.
   virtual void AdvanceTimeVaryingValuesToCurrentTime(GraphTime aCurrentTime,

dom/media/webaudio/AudioNodeEngine.h

@@ -333,6 +333,10 @@ class AudioNodeEngine {
   // returning false, then the stream can be suspended.
   virtual bool IsActive() const { return false; }
 
+  // Called on forced shutdown of the MediaStreamGraph before handing ownership
+  // from graph thread to main thread.
+  virtual void NotifyForcedShutdown() {}
+
   bool HasNode() const {
     MOZ_ASSERT(NS_IsMainThread());
     return !!mNode;

dom/media/webaudio/AudioNodeStream.cpp

@@ -52,6 +52,10 @@ AudioNodeStream::~AudioNodeStream() {
   MOZ_COUNT_DTOR(AudioNodeStream);
 }
 
+void AudioNodeStream::NotifyForcedShutdown() {
+  mEngine->NotifyForcedShutdown();
+}
+
 void AudioNodeStream::DestroyImpl() {
   // These are graph thread objects, so clean up on graph thread.
   mInputChunks.Clear();

dom/media/webaudio/AudioNodeStream.h

@@ -175,6 +175,7 @@ class AudioNodeStream : public ProcessedMediaStream {
   class AdvanceAndResumeMessage;
   class CheckForInactiveMessage;
 
+  void NotifyForcedShutdown() override;
   void DestroyImpl() override;
 
   /*
@@ -201,7 +202,7 @@ class AudioNodeStream : public ProcessedMediaStream {
   void DecrementActiveInputCount();
 
   // The engine that will generate output for this node.
-  nsAutoPtr<AudioNodeEngine> mEngine;
+  const nsAutoPtr<AudioNodeEngine> mEngine;
   // The mixed input blocks are kept from iteration to iteration to avoid
   // reallocating channel data arrays and any buffers for mixing.
   OutputChunks mInputChunks;

dom/media/webaudio/AudioWorkletNode.cpp

@@ -23,6 +23,8 @@ class WorkletNodeEngine final : public AudioNodeEngine {
   void ConstructProcessor(AudioWorkletImpl* aWorkletImpl,
                           const nsAString& aName,
                           StructuredCloneHolder* aOptionsSerialization);
+
+  void NotifyForcedShutdown() override {}
 };
 
 void WorkletNodeEngine::ConstructProcessor(