[iOS] keep threads merged when using Skia renderer on iOS (flutter/engine#54514)

Potential fix for money crasher.

engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_views_controller.h

@@ -84,14 +84,16 @@ class PlatformViewsController {
   ///
   /// Called from the raster thread.
   PostPrerollResult PostPrerollAction(
-      const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger);
+      const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger,
+      bool impeller_enabled);
 
   /// @brief Mark the end of a compositor frame.
   ///
   /// May determine changes are required to the thread merging state.
   /// Called from the raster thread.
   void EndFrame(bool should_resubmit_frame,
-                const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger);
+                const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger,
+                bool impeller_enabled);
 
   /// @brief Returns the Canvas for the overlay slice for the given platform view.
   ///

engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_views_controller.mm

@@ -15,13 +15,11 @@
 
 namespace {
 
-#ifdef FML_OS_IOS_SIMULATOR
 // The number of frames the rasterizer task runner will continue
 // to run on the platform thread after no platform view is rendered.
 //
 // Note: this is an arbitrary number.
 static const int kDefaultMergedLeaseDuration = 10;
-#endif  // FML_OS_IOS_SIMULATOR
 
 static constexpr NSUInteger kFlutterClippingMaskViewPoolCapacity = 5;
 
@@ -291,43 +289,52 @@ void PlatformViewsController::CancelFrame() {
 }
 
 PostPrerollResult PlatformViewsController::PostPrerollAction(
-    const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger) {
+    const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger,
+    bool impeller_enabled) {
   // TODO(jonahwilliams): remove this once Software backend is removed for iOS Sim.
 #ifdef FML_OS_IOS_SIMULATOR
-  if (composition_order_.empty()) {
+  const bool merge_threads = true;
-    return PostPrerollResult::kSuccess;
-  }
-  if (!raster_thread_merger->IsMerged()) {
-    // The raster thread merger may be disabled if the rasterizer is being
-    // created or teared down.
-    //
-    // In such cases, the current frame is dropped, and a new frame is attempted
-    // with the same layer tree.
-    //
-    // Eventually, the frame is submitted once this method returns `kSuccess`.
-    // At that point, the raster tasks are handled on the platform thread.
-    CancelFrame();
-    return PostPrerollResult::kSkipAndRetryFrame;
-  }
-  // If the post preroll action is successful, we will display platform views in the current frame.
-  // In order to sync the rendering of the platform views (quartz) with skia's rendering,
-  // We need to begin an explicit CATransaction. This transaction needs to be submitted
-  // after the current frame is submitted.
-  raster_thread_merger->ExtendLeaseTo(kDefaultMergedLeaseDuration);
-  return PostPrerollResult::kSuccess;
 #else
-  return PostPrerollResult::kSuccess;
+  const bool merge_threads = !impeller_enabled;
 #endif  // FML_OS_IOS_SIMULATOR
+
+  if (merge_threads) {
+    if (composition_order_.empty()) {
+      return PostPrerollResult::kSuccess;
+    }
+    if (!raster_thread_merger->IsMerged()) {
+      // The raster thread merger may be disabled if the rasterizer is being
+      // created or teared down.
+      //
+      // In such cases, the current frame is dropped, and a new frame is attempted
+      // with the same layer tree.
+      //
+      // Eventually, the frame is submitted once this method returns `kSuccess`.
+      // At that point, the raster tasks are handled on the platform thread.
+      CancelFrame();
+      return PostPrerollResult::kSkipAndRetryFrame;
+    }
+    // If the post preroll action is successful, we will display platform views in the current
+    // frame. In order to sync the rendering of the platform views (quartz) with skia's rendering,
+    // We need to begin an explicit CATransaction. This transaction needs to be submitted
+    // after the current frame is submitted.
+    raster_thread_merger->ExtendLeaseTo(kDefaultMergedLeaseDuration);
+  }
+  return PostPrerollResult::kSuccess;
 }
 
 void PlatformViewsController::EndFrame(
     bool should_resubmit_frame,
-    const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger) {
+    const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger,
+    bool impeller_enabled) {
 #if FML_OS_IOS_SIMULATOR
-  if (should_resubmit_frame) {
+  bool run_check = true;
+#else
+  bool run_check = !impeller_enabled;
+#endif  // FML_OS_IOS_SIMULATOR
+  if (run_check && should_resubmit_frame) {
     raster_thread_merger->MergeWithLease(kDefaultMergedLeaseDuration);
   }
-#endif  // FML_OS_IOS_SIMULATOR
 }
 
 void PlatformViewsController::PushFilterToVisitedPlatformViews(

engine/src/flutter/shell/platform/darwin/ios/ios_external_view_embedder.mm

@@ -59,7 +59,8 @@ PostPrerollResult IOSExternalViewEmbedder::PostPrerollAction(
     const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger) {
   TRACE_EVENT0("flutter", "IOSExternalViewEmbedder::PostPrerollAction");
   FML_CHECK(platform_views_controller_);
-  PostPrerollResult result = platform_views_controller_->PostPrerollAction(raster_thread_merger);
+  PostPrerollResult result = platform_views_controller_->PostPrerollAction(
+      raster_thread_merger, ios_context_->GetBackend() != IOSRenderingBackend::kSkia);
   return result;
 }
 
@@ -91,7 +92,8 @@ void IOSExternalViewEmbedder::EndFrame(
     bool should_resubmit_frame,
     const fml::RefPtr<fml::RasterThreadMerger>& raster_thread_merger) {
   TRACE_EVENT0("flutter", "IOSExternalViewEmbedder::EndFrame");
-  platform_views_controller_->EndFrame(should_resubmit_frame, raster_thread_merger);
+  platform_views_controller_->EndFrame(should_resubmit_frame, raster_thread_merger,
+                                       ios_context_->GetBackend() != IOSRenderingBackend::kSkia);
 }
 
 // |ExternalViewEmbedder|
@@ -100,7 +102,7 @@ bool IOSExternalViewEmbedder::SupportsDynamicThreadMerging() {
 #if FML_OS_IOS_SIMULATOR
   return true;
 #else
-  return false;
+  return ios_context_->GetBackend() == IOSRenderingBackend::kSkia;
 #endif  // FML_OS_IOS_SIMULATOR
 }