only add transcations on main thread

Author: Chris Yang

shell/platform/darwin/ios/ios_surface.mm

@@ -71,9 +71,11 @@
   TRACE_EVENT0("flutter", "IOSSurface::CancelFrame");
   FML_CHECK(platform_views_controller_ != nullptr);
   platform_views_controller_->CancelFrame();
-  // Committing the current transaction as |BeginFrame| will create a nested
-  // CATransaction otherwise.
-  [CATransaction commit];
+  if ([[NSThread currentThread] isMainThread]) {
+    // Committing the current transaction as |BeginFrame| will create a nested
+    // CATransaction otherwise.
+    [CATransaction commit];
+  }
 }
 
 // |ExternalViewEmbedder|
@@ -84,7 +86,9 @@
   TRACE_EVENT0("flutter", "IOSSurface::BeginFrame");
   FML_CHECK(platform_views_controller_ != nullptr);
   platform_views_controller_->SetFrameSize(frame_size);
-  [CATransaction begin];
+  if ([[NSThread currentThread] isMainThread]) {
+    [CATransaction begin];
+  }
 }
 
 // |ExternalViewEmbedder|
@@ -102,7 +106,7 @@
   TRACE_EVENT0("flutter", "IOSSurface::PostPrerollAction");
   FML_CHECK(platform_views_controller_ != nullptr);
   PostPrerollResult result = platform_views_controller_->PostPrerollAction(raster_thread_merger);
-  if (result == PostPrerollResult::kSkipAndRetryFrame) {
+  if (result == PostPrerollResult::kSkipAndRetryFrame && [[NSThread currentThread] isMainThread]) {
     // Commit the current transaction if the frame is dropped.
     [CATransaction commit];
   }
@@ -129,7 +133,7 @@
   bool submitted =
       platform_views_controller_->SubmitFrame(std::move(context), ios_context_, std::move(frame));
 
-  if (submitted) {
+  if (submitted && [[NSThread currentThread] isMainThread]) {
     TRACE_EVENT0("flutter", "IOSSurface::DidSubmitFrame");
     [CATransaction commit];
   }