Remove tear_down_mutex_ from BaseAudioContext

In favor of the self-referencing patch, this mutex can be safely
removed.

Test: Ran the patch on a repro case from crbug.com/1029462 and saw no crash after 20 min.
Bug: 1058555
Change-Id: I0335fa6c878f4ca7e52a03ed7eb6fc0891dfa3ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2088491Reviewed-by: Raymond Toy <rtoy@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748376}

third_party/blink/renderer/modules/webaudio/base_audio_context.cc

@@ -150,8 +150,6 @@ void BaseAudioContext::Clear() {
 void BaseAudioContext::Uninitialize() {
   DCHECK(IsMainThread());
 
-  MutexLocker locker(GetTearDownMutex());
-
   if (!IsDestinationInitialized())
     return;
 

third_party/blink/renderer/modules/webaudio/base_audio_context.h

@@ -328,8 +328,6 @@ class MODULES_EXPORT BaseAudioContext
   void ReportDidCreate() final;
   void ReportWillBeDestroyed() final;
 
-  Mutex& GetTearDownMutex() const { return tear_down_mutex_; }
-
  protected:
   enum ContextType { kRealtimeContext, kOfflineContext };
 
@@ -431,12 +429,6 @@ class MODULES_EXPORT BaseAudioContext
   // This cannot be nullptr once it is assigned from AudioWorkletThread until
   // the BaseAudioContext goes away.
   WorkerThread* audio_worklet_thread_ = nullptr;
-
-  // Due to the multi-threading architecture of WebAudio, it is possible that
-  // object allocated by the main thread still can be accessed by the audio
-  // rendering thread while this context is torn down (GCed) by
-  // |Uninitialize()|.
-  mutable Mutex tear_down_mutex_;
 };
 
 }  // namespace blink

third_party/blink/renderer/modules/webaudio/offline_audio_destination_node.cc

@@ -293,33 +293,25 @@ bool OfflineAudioDestinationHandler::RenderIfNotSuspended(
     return true;
   }
 
-  {
-    MutexTryLocker try_locker(Context()->GetTearDownMutex());
-    if (try_locker.Locked()) {
-      DCHECK_GE(NumberOfInputs(), 1u);
-
-      // This will cause the node(s) connected to us to process, which in turn
-      // will pull on their input(s), all the way backwards through the
-      // rendering graph.
-      scoped_refptr<AudioBus> rendered_bus =
-          Input(0).Pull(destination_bus, number_of_frames);
-
-      if (!rendered_bus) {
-        destination_bus->Zero();
-      } else if (rendered_bus != destination_bus) {
-        // in-place processing was not possible - so copy
-        destination_bus->CopyFrom(*rendered_bus);
-      }
-    } else {
-      destination_bus->Zero();
-    }
+  DCHECK_GE(NumberOfInputs(), 1u);
 
-    // Process nodes which need a little extra help because they are not
-    // connected to anything, but still need to process.
-    Context()->GetDeferredTaskHandler().ProcessAutomaticPullNodes(
-        number_of_frames);
+  // This will cause the node(s) connected to us to process, which in turn will
+  // pull on their input(s), all the way backwards through the rendering graph.
+  scoped_refptr<AudioBus> rendered_bus =
+      Input(0).Pull(destination_bus, number_of_frames);
+
+  if (!rendered_bus) {
+    destination_bus->Zero();
+  } else if (rendered_bus != destination_bus) {
+    // in-place processing was not possible - so copy
+    destination_bus->CopyFrom(*rendered_bus);
   }
 
+  // Process nodes which need a little extra help because they are not connected
+  // to anything, but still need to process.
+  Context()->GetDeferredTaskHandler().ProcessAutomaticPullNodes(
+      number_of_frames);
+
   // Let the context take care of any business at the end of each render
   // quantum.
   Context()->HandlePostRenderTasks();

third_party/blink/renderer/modules/webaudio/realtime_audio_destination_node.cc

@@ -198,35 +198,30 @@ void RealtimeAudioDestinationHandler::Render(
   // Only pull on the audio graph if we have not stopped the destination.  It
   // takes time for the destination to stop, but we want to stop pulling before
   // the destination has actually stopped.
-  {
-    MutexTryLocker try_locker(context->GetTearDownMutex());
-    if (try_locker.Locked() && IsPullingAudioGraphAllowed()) {
-      // Renders the graph by pulling all the inputs to this node. This will
-      // in turn pull on their inputs, all the way backwards through the graph.
-      scoped_refptr<AudioBus> rendered_bus =
-          Input(0).Pull(destination_bus, number_of_frames);
-
-      DCHECK(rendered_bus);
-      if (!rendered_bus) {
-        // AudioNodeInput might be in the middle of destruction. Then the
-        // internal summing bus will return as nullptr. Then zero out the
-        // output.
-        destination_bus->Zero();
-      } else if (rendered_bus != destination_bus) {
-        // In-place processing was not possible. Copy the rendererd result to
-        // the given |destination_bus| buffer.
-        destination_bus->CopyFrom(*rendered_bus);
-      }
-    } else {
+  if (IsPullingAudioGraphAllowed()) {
+    // Renders the graph by pulling all the inputs to this node. This will in
+    // turn pull on their inputs, all the way backwards through the graph.
+    scoped_refptr<AudioBus> rendered_bus =
+        Input(0).Pull(destination_bus, number_of_frames);
+
+    DCHECK(rendered_bus);
+    if (!rendered_bus) {
+      // AudioNodeInput might be in the middle of destruction. Then the internal
+      // summing bus will return as nullptr. Then zero out the output.
       destination_bus->Zero();
+    } else if (rendered_bus != destination_bus) {
+      // In-place processing was not possible. Copy the rendered result to the
+      // given |destination_bus| buffer.
+      destination_bus->CopyFrom(*rendered_bus);
     }
-
-    // Processes "automatic" nodes that are not connected to anything. This can
-    // be done after copying because it does not affect the rendered result.
-    context->GetDeferredTaskHandler().ProcessAutomaticPullNodes(
-        number_of_frames);
+  } else {
+    destination_bus->Zero();
   }
 
+  // Processes "automatic" nodes that are not connected to anything. This can
+  // be done after copying because it does not affect the rendered result.
+  context->GetDeferredTaskHandler().ProcessAutomaticPullNodes(number_of_frames);
+
   context->HandlePostRenderTasks();
 
   context->HandleAudibility(destination_bus);