Add flushUIThreadTasks service RPC

shell/common/platform_view_service_protocol.cc

@@ -128,6 +128,9 @@ void PlatformViewServiceProtocol::RegisterHook(bool running_precompiled_code) {
   }
   Dart_RegisterRootServiceRequestCallback(kRunInViewExtensionName, &RunInView,
                                           nullptr);
+  // [benchmark helper] Wait for the UI Thread to idle.
+  Dart_RegisterRootServiceRequestCallback(kWaitUIThreadIdleExtensionName,
+                                          &WaitUIThreadIdle, nullptr);
 }
 
 const char* PlatformViewServiceProtocol::kRunInViewExtensionName =
@@ -202,11 +205,10 @@ bool PlatformViewServiceProtocol::ListViews(const char* method,
                                             intptr_t num_params,
                                             void* user_data,
                                             const char** json_object) {
-  // Ask the Shell for the list of platform views. This will run a task on
-  // the UI thread before returning.
+  // Ask the Shell for the list of platform views.
   Shell& shell = Shell::Shared();
   std::vector<Shell::PlatformViewInfo> platform_views;
-  shell.WaitForPlatformViewIds(&platform_views);
+  shell.GetPlatformViewIds(&platform_views);
 
   std::stringstream response;
 
@@ -314,4 +316,29 @@ void PlatformViewServiceProtocol::ScreenshotGpuTask(SkBitmap* bitmap) {
   canvas->flush();
 }
 
+const char* PlatformViewServiceProtocol::kWaitUIThreadIdleExtensionName =
+    "_flutter.waitUIThreadIdle";
+
+// This API should not be invoked by production code.
+// It can potentially starve the service isolate if the main isolate pauses
+// at a breakpoint or is in an infinite loop.
+bool PlatformViewServiceProtocol::WaitUIThreadIdle(const char* method,
+                                                   const char** param_keys,
+                                                   const char** param_values,
+                                                   intptr_t num_params,
+                                                   void* user_data,
+                                                   const char** json_object) {
+  ftl::AutoResetWaitableEvent latch;
+  blink::Threads::UI()->PostTask([&latch]() {
+    // This task is empty because we just need to synchronize this RPC with the
+    // UI Thread
+    latch.Signal();
+  });
+
+  latch.Wait();
+
+  *json_object = strdup("{\"type\":\"Success\"}");
+  return true;
+}
+
 }  // namespace shell

shell/common/platform_view_service_protocol.h

@@ -43,6 +43,17 @@ class PlatformViewServiceProtocol {
                          void* user_data,
                          const char** json_object);
   static void ScreenshotGpuTask(SkBitmap* bitmap);
+
+  // This API should not be invoked by production code.
+  // It can potentially starve the service isolate if the main isolate pauses
+  // at a breakpoint or is in an infinite loop.
+  static const char* kWaitUIThreadIdleExtensionName;
+  static bool WaitUIThreadIdle(const char* method,
+                               const char** param_keys,
+                               const char** param_values,
+                               intptr_t num_params,
+                               void* user_data,
+                               const char** json_object);
 };
 
 }  // namespace shell

shell/common/shell.cc

@@ -262,7 +262,7 @@ void Shell::GetPlatformViews(
   *platform_views = platform_views_;
 }
 
-void Shell::WaitForPlatformViewIds(
+void Shell::GetPlatformViewIds(
     std::vector<PlatformViewInfo>* platform_view_ids) {
   std::lock_guard<std::mutex> lk(platform_views_mutex_);
   for (auto it = platform_views_.begin(); it != platform_views_.end(); it++) {

shell/common/shell.h

@@ -44,7 +44,7 @@ class Shell {
 
   // List of PlatformViews.
 
-  // These APIs must only be accessed on UI thread.
+  // These APIs can be called from any thread.
   void AddPlatformView(const std::shared_ptr<PlatformView>& platform_view);
   void PurgePlatformViews();
   void GetPlatformViews(
@@ -58,7 +58,7 @@ class Shell {
 
   // These APIs can be called from any thread.
   // Return the list of platform view ids at the time of this call.
-  void WaitForPlatformViewIds(std::vector<PlatformViewInfo>* platform_view_ids);
+  void GetPlatformViewIds(std::vector<PlatformViewInfo>* platform_view_ids);
 
   // Attempt to run a script inside a flutter view indicated by |view_id|.
   // Will set |view_existed| to true if the view was found and false otherwise.