Android platform view static thread merging

common/settings.h

@@ -213,6 +213,15 @@ struct Settings {
   /// to log a timeline event that tracks the latency of engine startup.
   std::chrono::microseconds engine_start_timestamp = {};
 
+  /// Whether the application claims that it uses the android embedded view for
+  /// platform views.
+  ///
+  /// A `true` value will result the raster task runner always run on the
+  /// platform thread.
+  // TODO(cyanlaz): Remove this when dynamic thread merging is done.
+  // https://github.com/flutter/flutter/issues/59930
+  bool use_embedded_view = false;
+
   std::string ToString() const;
 };
 

shell/common/switches.cc

@@ -227,6 +227,9 @@ Settings SettingsFromCommandLine(const fml::CommandLine& command_line) {
                                                             : "127.0.0.1";
   }
 
+  settings.use_embedded_view =
+      command_line.HasOption(FlagForSwitch(Switch::UseEmbeddedView));
+
   // Set Observatory Port
   if (command_line.HasOption(FlagForSwitch(Switch::DeviceObservatoryPort))) {
     if (!GetSwitchValue(command_line, Switch::DeviceObservatoryPort,

shell/common/switches.h

@@ -189,6 +189,15 @@ DEF_SWITCH(
     "Uses separate threads for the platform, UI, GPU and IO task runners. "
     "By default, a single thread is used for all task runners. Only available "
     "in the flutter_tester.")
+// TODO(cyanlaz): Remove this when dynamic thread merging is done.
+// https://github.com/flutter/flutter/issues/59930
+DEF_SWITCH(UseEmbeddedView,
+           "use-embedded-view",
+           "Whether an android application uses embedded views."
+           "This is a temporary flag to make the raster task runner runs on "
+           "the platform thread."
+           "This flag should be removed once the dynamic thread merging is "
+           "enabled on android.")
 DEF_SWITCHES_END
 
 void PrintUsage(const std::string& executable_name);

shell/platform/android/android_shell_holder.cc

@@ -28,6 +28,8 @@ static WindowData GetDefaultWindowData() {
   return window_data;
 }
 
+bool AndroidShellHolder::use_embedded_view;
+
 AndroidShellHolder::AndroidShellHolder(
     flutter::Settings settings,
     std::shared_ptr<PlatformViewAndroidJNI> jni_facade,
@@ -101,28 +103,55 @@ AndroidShellHolder::AndroidShellHolder(
     ui_runner = thread_host_.ui_thread->GetTaskRunner();
     io_runner = thread_host_.io_thread->GetTaskRunner();
   }
-  flutter::TaskRunners task_runners(thread_label,     // label
-                                    platform_runner,  // platform
-                                    gpu_runner,       // raster
-                                    ui_runner,        // ui
-                                    io_runner         // io
-  );
-
-  shell_ =
-      Shell::Create(task_runners,             // task runners
-                    GetDefaultWindowData(),   // window data
-                    settings_,                // settings
-                    on_create_platform_view,  // platform view create callback
-                    on_create_rasterizer      // rasterizer create callback
-      );
+  if (settings.use_embedded_view) {
+    use_embedded_view = true;
+    // Embedded views requires the gpu and the platform views to be the same.
+    // The plan is to eventually dynamically merge the threads when there's a
+    // platform view in the layer tree.
+    // For now we use a fixed thread configuration with the same thread used as
+    // the gpu and platform task runner.
+    // TODO(amirh/chinmaygarde): remove this, and dynamically change the thread
+    // configuration. https://github.com/flutter/flutter/issues/23975
+    // https://github.com/flutter/flutter/issues/59930
+    flutter::TaskRunners task_runners(thread_label,     // label
+                                      platform_runner,  // platform
+                                      platform_runner,  // raster
+                                      ui_runner,        // ui
+                                      io_runner         // io
+    );
+
+    shell_ =
+        Shell::Create(task_runners,             // task runners
+                      GetDefaultWindowData(),   // window data
+                      settings_,                // settings
+                      on_create_platform_view,  // platform view create callback
+                      on_create_rasterizer      // rasterizer create callback
+        );
+  } else {
+    use_embedded_view = false;
+    flutter::TaskRunners task_runners(thread_label,     // label
+                                      platform_runner,  // platform
+                                      gpu_runner,       // raster
+                                      ui_runner,        // ui
+                                      io_runner         // io
+    );
+
+    shell_ =
+        Shell::Create(task_runners,             // task runners
+                      GetDefaultWindowData(),   // window data
+                      settings_,                // settings
+                      on_create_platform_view,  // platform view create callback
+                      on_create_rasterizer      // rasterizer create callback
+        );
+  }
 
   platform_view_ = weak_platform_view;
   FML_DCHECK(platform_view_);
 
   is_valid_ = shell_ != nullptr;
 
   if (is_valid_) {
-    task_runners.GetRasterTaskRunner()->PostTask([]() {
+    shell_->GetTaskRunners().GetRasterTaskRunner()->PostTask([]() {
       // Android describes -8 as "most important display threads, for
       // compositing the screen and retrieving input events". Conservatively
       // set the raster thread to slightly lower priority than it.
@@ -134,7 +163,7 @@ AndroidShellHolder::AndroidShellHolder(
         }
       }
     });
-    task_runners.GetUITaskRunner()->PostTask([]() {
+    shell_->GetTaskRunners().GetUITaskRunner()->PostTask([]() {
       if (::setpriority(PRIO_PROCESS, gettid(), -1) != 0) {
         FML_LOG(ERROR) << "Failed to set UI task runner priority";
       }

shell/platform/android/android_shell_holder.h

@@ -21,6 +21,14 @@ namespace flutter {
 
 class AndroidShellHolder {
  public:
+  // Whether the application sets to use embedded_view view
+  // `io.flutter.embedded_views_preview` flag. This can be static because it is
+  // determined by the application and it is safe when there are multiple
+  // `AndroidSurface`s.
+  // TODO(cyanglaz): remove this when dynamic thread merging is enabled on
+  // android. https://github.com/flutter/flutter/issues/59930
+  static bool use_embedded_view;
+
   AndroidShellHolder(flutter::Settings settings,
                      std::shared_ptr<PlatformViewAndroidJNI> jni_facade,
                      bool is_background_view);

shell/platform/android/android_surface_gl.cc

@@ -8,6 +8,7 @@
 
 #include "flutter/fml/logging.h"
 #include "flutter/fml/memory/ref_ptr.h"
+#include "flutter/shell/platform/android/android_shell_holder.h"
 
 namespace flutter {
 
@@ -122,6 +123,9 @@ intptr_t AndroidSurfaceGL::GLContextFBO() const {
 
 // |GPUSurfaceGLDelegate|
 ExternalViewEmbedder* AndroidSurfaceGL::GetExternalViewEmbedder() {
+  if (!AndroidShellHolder::use_embedded_view) {
+    return nullptr;
+  }
   return external_view_embedder_.get();
 }
 

shell/platform/android/android_surface_software.cc

@@ -11,6 +11,7 @@
 #include "flutter/fml/platform/android/jni_weak_ref.h"
 #include "flutter/fml/platform/android/scoped_java_ref.h"
 #include "flutter/fml/trace_event.h"
+#include "flutter/shell/platform/android/android_shell_holder.h"
 #include "flutter/shell/platform/android/jni/platform_view_android_jni.h"
 
 namespace flutter {
@@ -145,6 +146,9 @@ bool AndroidSurfaceSoftware::PresentBackingStore(
 
 // |GPUSurfaceSoftwareDelegate|
 ExternalViewEmbedder* AndroidSurfaceSoftware::GetExternalViewEmbedder() {
+  if (!AndroidShellHolder::use_embedded_view) {
+    return nullptr;
+  }
   return external_view_embedder_.get();
 }
 

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

@@ -201,7 +201,6 @@ public void ensureInitializationComplete(
               + applicationInfo.nativeLibraryDir
               + File.separator
               + DEFAULT_LIBRARY);
-
       if (args != null) {
         Collections.addAll(shellArgs, args);
       }
@@ -234,6 +233,17 @@ public void ensureInitializationComplete(
       }
 
       long initTimeMillis = SystemClock.uptimeMillis() - initStartTimestampMillis;
+
+      // TODO(cyanlaz): Remove this when dynamic thread merging is done.
+      // https://github.com/flutter/flutter/issues/59930
+      Bundle bundle = applicationInfo.metaData;
+      if (bundle != null) {
+        boolean use_embedded_view = bundle.getBoolean("io.flutter.embedded_views_preview");
+        if (use_embedded_view) {
+          shellArgs.add("--use-embedded-view");
+        }
+      }
+
       FlutterJNI.nativeInit(
           applicationContext,
           shellArgs.toArray(new String[0]),

shell/platform/android/platform_view_android.h

@@ -117,7 +117,6 @@ class PlatformViewAndroid final : public PlatformView {
 
   FML_DISALLOW_COPY_AND_ASSIGN(PlatformViewAndroid);
 };
-
 }  // namespace flutter
 
 #endif  // SHELL_PLATFORM_ANDROID_PLATFORM_VIEW_ANDROID_H_

testing/scenario_app/android/app/src/main/AndroidManifest.xml

@@ -28,6 +28,9 @@
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
         </activity>
+        <meta-data
+            android:name="io.flutter.embedded_views_preview"
+            android:value="true" />
     </application>
 
     <uses-permission android:name="android.permission.INTERNET" />