[Impeller] reland: defer impeller context initialization onto the raster thread. (#167765)

Attempt to speed up vulkan startup by ensuring vulkan driver
initialization happens on raster thread. Prev. we immediately
initialized the impeller::Context, unfortunately setting up the vulkan
context can take upwards of 100ms. This time is running on the platform
thread and blocking startup.

Instead, I attempt to hide/defer as much as possible what backend is
being used - this requires us to access the impeller context via a
shared_future in some cases instead of immediately knowing it is valid.

Author: Jonah Williams

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -51891,7 +51891,6 @@ ORIGIN: ../../../flutter/lib/ui/dart_wrapper.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/floating_point.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/geometry.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/hooks.dart + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/lib/ui/io_manager.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/io_manager.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/isolate_name_server.dart + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/lib/ui/isolate_name_server/isolate_name_server.cc + ../../../flutter/LICENSE
@@ -52425,6 +52424,8 @@ ORIGIN: ../../../flutter/shell/gpu/gpu_surface_vulkan_delegate.h + ../../../flut
 ORIGIN: ../../../flutter/shell/gpu/gpu_surface_vulkan_impeller.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/gpu/gpu_surface_vulkan_impeller.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/AndroidManifest.xml + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/android_context_dynamic_impeller.cc + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/android_context_dynamic_impeller.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_context_gl_impeller.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_context_gl_impeller.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_context_gl_skia.cc + ../../../flutter/LICENSE
@@ -52443,6 +52444,8 @@ ORIGIN: ../../../flutter/shell/platform/android/android_image_generator.h + ../.
 ORIGIN: ../../../flutter/shell/platform/android/android_rendering_selector.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_shell_holder.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_shell_holder.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/android_surface_dynamic_impeller.cc + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/android_surface_dynamic_impeller.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_surface_gl_impeller.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_surface_gl_impeller.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/android_surface_gl_skia.cc + ../../../flutter/LICENSE
@@ -52459,6 +52462,8 @@ ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_
 ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_wrapper.cc + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_wrapper.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/surface_pool.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/external_view_embedder/surface_pool.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/android/flutter_main.cc + ../../../flutter/LICENSE
@@ -54883,7 +54888,6 @@ FILE: ../../../flutter/lib/ui/dart_wrapper.h
 FILE: ../../../flutter/lib/ui/floating_point.h
 FILE: ../../../flutter/lib/ui/geometry.dart
 FILE: ../../../flutter/lib/ui/hooks.dart
-FILE: ../../../flutter/lib/ui/io_manager.cc
 FILE: ../../../flutter/lib/ui/io_manager.h
 FILE: ../../../flutter/lib/ui/isolate_name_server.dart
 FILE: ../../../flutter/lib/ui/isolate_name_server/isolate_name_server.cc
@@ -55418,6 +55422,8 @@ FILE: ../../../flutter/shell/gpu/gpu_surface_vulkan_delegate.h
 FILE: ../../../flutter/shell/gpu/gpu_surface_vulkan_impeller.cc
 FILE: ../../../flutter/shell/gpu/gpu_surface_vulkan_impeller.h
 FILE: ../../../flutter/shell/platform/android/AndroidManifest.xml
+FILE: ../../../flutter/shell/platform/android/android_context_dynamic_impeller.cc
+FILE: ../../../flutter/shell/platform/android/android_context_dynamic_impeller.h
 FILE: ../../../flutter/shell/platform/android/android_context_gl_impeller.cc
 FILE: ../../../flutter/shell/platform/android/android_context_gl_impeller.h
 FILE: ../../../flutter/shell/platform/android/android_context_gl_skia.cc
@@ -55436,6 +55442,8 @@ FILE: ../../../flutter/shell/platform/android/android_image_generator.h
 FILE: ../../../flutter/shell/platform/android/android_rendering_selector.h
 FILE: ../../../flutter/shell/platform/android/android_shell_holder.cc
 FILE: ../../../flutter/shell/platform/android/android_shell_holder.h
+FILE: ../../../flutter/shell/platform/android/android_surface_dynamic_impeller.cc
+FILE: ../../../flutter/shell/platform/android/android_surface_dynamic_impeller.h
 FILE: ../../../flutter/shell/platform/android/android_surface_gl_impeller.cc
 FILE: ../../../flutter/shell/platform/android/android_surface_gl_impeller.h
 FILE: ../../../flutter/shell/platform/android/android_surface_gl_skia.cc
@@ -55452,6 +55460,8 @@ FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_vi
 FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder.h
 FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.cc
 FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.h
+FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_wrapper.cc
+FILE: ../../../flutter/shell/platform/android/external_view_embedder/external_view_embedder_wrapper.h
 FILE: ../../../flutter/shell/platform/android/external_view_embedder/surface_pool.cc
 FILE: ../../../flutter/shell/platform/android/external_view_embedder/surface_pool.h
 FILE: ../../../flutter/shell/platform/android/flutter_main.cc

engine/src/flutter/impeller/renderer/context.cc

@@ -4,10 +4,24 @@
 
 #include "impeller/renderer/context.h"
 
+#include <mutex>
 #include <utility>
 
 namespace impeller {
 
+ImpellerContextFuture::ImpellerContextFuture(
+    std::future<std::shared_ptr<impeller::Context>> context)
+    : future_(std::move(context)) {}
+
+std::shared_ptr<impeller::Context> ImpellerContextFuture::GetContext() {
+  std::scoped_lock<std::mutex> lock(mutex_);
+  if (!did_wait_ && future_.valid()) {
+    context_ = future_.get();
+    did_wait_ = true;
+  }
+  return context_;
+}
+
 Context::~Context() = default;
 
 Context::Context(const Flags& flags) : flags_(flags) {}

engine/src/flutter/impeller/renderer/context.h

@@ -5,11 +5,13 @@
 #ifndef FLUTTER_IMPELLER_RENDERER_CONTEXT_H_
 #define FLUTTER_IMPELLER_RENDERER_CONTEXT_H_
 
+#include <future>
 #include <memory>
 #include <string>
 
 #include "fml/closure.h"
 #include "impeller/base/flags.h"
+#include "impeller/base/thread_safety.h"
 #include "impeller/core/allocator.h"
 #include "impeller/core/formats.h"
 #include "impeller/renderer/capabilities.h"
@@ -22,6 +24,22 @@ class ShaderLibrary;
 class CommandBuffer;
 class PipelineLibrary;
 
+/// A wrapper for provided a deferred initialization of impeller to various
+/// engine subsystems.
+class ImpellerContextFuture {
+ public:
+  explicit ImpellerContextFuture(
+      std::future<std::shared_ptr<impeller::Context>> context);
+
+  std::shared_ptr<impeller::Context> GetContext();
+
+ private:
+  std::mutex mutex_;
+  std::future<std::shared_ptr<impeller::Context>> future_;
+  std::shared_ptr<impeller::Context> context_;
+  bool did_wait_ = false;
+};
+
 //------------------------------------------------------------------------------
 /// @brief      To do anything rendering related with Impeller, you need a
 ///             context.

engine/src/flutter/lib/ui/BUILD.gn

@@ -38,7 +38,6 @@ source_set("ui") {
     "dart_ui.h",
     "dart_wrapper.h",
     "floating_point.h",
-    "io_manager.cc",
     "io_manager.h",
     "isolate_name_server/isolate_name_server.cc",
     "isolate_name_server/isolate_name_server.h",

engine/src/flutter/lib/ui/io_manager.cc

@@ -31,7 +31,10 @@ class IOManager {
   virtual std::shared_ptr<const fml::SyncSwitch>
   GetIsGpuDisabledSyncSwitch() = 0;
 
-  virtual std::shared_ptr<impeller::Context> GetImpellerContext() const;
+  /// @brief Retrieve the impeller::Context.
+  ///
+  /// Call may block until context is availabe.
+  virtual std::shared_ptr<impeller::Context> GetImpellerContext() const = 0;
 };
 
 }  // namespace flutter

engine/src/flutter/lib/ui/io_manager.h

@@ -105,8 +105,11 @@ ImageDecoderImpeller::ImageDecoderImpeller(
   context_ = context_promise.get_future();
   runners_.GetIOTaskRunner()->PostTask(fml::MakeCopyable(
       [promise = std::move(context_promise), io_manager]() mutable {
-        promise.set_value(io_manager ? io_manager->GetImpellerContext()
-                                     : nullptr);
+        if (io_manager) {
+          promise.set_value(io_manager->GetImpellerContext());
+        } else {
+          promise.set_value(nullptr);
+        }
       }));
 }
 

engine/src/flutter/lib/ui/painting/image_decoder_impeller.cc

@@ -31,9 +31,9 @@ UIDartState::Context::Context(
     std::string advisory_script_entrypoint,
     bool deterministic_rendering_enabled,
     std::shared_ptr<fml::ConcurrentTaskRunner> concurrent_task_runner,
+    std::shared_future<impeller::RuntimeStageBackend> runtime_stage_backend,
     bool enable_impeller,
-    bool enable_flutter_gpu,
-    impeller::RuntimeStageBackend runtime_stage_backend)
+    bool enable_flutter_gpu)
     : task_runners(task_runners),
       snapshot_delegate(std::move(snapshot_delegate)),
       io_manager(std::move(io_manager)),
@@ -44,9 +44,9 @@ UIDartState::Context::Context(
       advisory_script_entrypoint(std::move(advisory_script_entrypoint)),
       deterministic_rendering_enabled(deterministic_rendering_enabled),
       concurrent_task_runner(std::move(concurrent_task_runner)),
+      runtime_stage_backend(std::move(runtime_stage_backend)),
       enable_impeller(enable_impeller),
-      enable_flutter_gpu(enable_flutter_gpu),
-      runtime_stage_backend(runtime_stage_backend) {}
+      enable_flutter_gpu(enable_flutter_gpu) {}
 
 UIDartState::UIDartState(
     TaskObserverAdd add_callback,
@@ -88,10 +88,6 @@ bool UIDartState::IsFlutterGPUEnabled() const {
   return context_.enable_impeller && context_.enable_flutter_gpu;
 }
 
-impeller::RuntimeStageBackend UIDartState::GetRuntimeStageBackend() const {
-  return context_.runtime_stage_backend;
-}
-
 void UIDartState::DidSetIsolate() {
   main_port_ = Dart_GetMainPortId();
   std::ostringstream debug_name;
@@ -253,4 +249,9 @@ Dart_Isolate UIDartState::CreatePlatformIsolate(Dart_Handle entry_point,
   return nullptr;
 }
 
+/// The runtime stage to use for fragment shaders.
+impeller::RuntimeStageBackend UIDartState::GetRuntimeStageBackend() const {
+  return context_.runtime_stage_backend.get();
+}
+
 }  // namespace flutter

engine/src/flutter/lib/ui/ui_dart_state.cc

@@ -5,6 +5,7 @@
 #ifndef FLUTTER_LIB_UI_UI_DART_STATE_H_
 #define FLUTTER_LIB_UI_UI_DART_STATE_H_
 
+#include <future>
 #include <memory>
 #include <string>
 #include <utility>
@@ -19,6 +20,7 @@
 #include "flutter/lib/ui/painting/image_decoder.h"
 #include "flutter/lib/ui/snapshot_delegate.h"
 #include "flutter/shell/common/platform_message_handler.h"
+#include "impeller/core/runtime_types.h"
 #include "impeller/runtime_stage/runtime_stage.h"
 #include "third_party/dart/runtime/include/dart_api.h"
 #include "third_party/skia/include/gpu/ganesh/GrDirectContext.h"
@@ -44,20 +46,21 @@ class UIDartState : public tonic::DartState {
   struct Context {
     explicit Context(const TaskRunners& task_runners);
 
-    Context(const TaskRunners& task_runners,
-            fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate,
-            fml::WeakPtr<IOManager> io_manager,
-            fml::RefPtr<SkiaUnrefQueue> unref_queue,
-            fml::TaskRunnerAffineWeakPtr<ImageDecoder> image_decoder,
-            fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
-                image_generator_registry,
-            std::string advisory_script_uri,
-            std::string advisory_script_entrypoint,
-            bool deterministic_rendering_enabled,
-            std::shared_ptr<fml::ConcurrentTaskRunner> concurrent_task_runner,
-            bool enable_impeller,
-            bool enable_flutter_gpu,
-            impeller::RuntimeStageBackend runtime_stage_backend);
+    Context(
+        const TaskRunners& task_runners,
+        fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate,
+        fml::WeakPtr<IOManager> io_manager,
+        fml::RefPtr<SkiaUnrefQueue> unref_queue,
+        fml::TaskRunnerAffineWeakPtr<ImageDecoder> image_decoder,
+        fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
+            image_generator_registry,
+        std::string advisory_script_uri,
+        std::string advisory_script_entrypoint,
+        bool deterministic_rendering_enabled,
+        std::shared_ptr<fml::ConcurrentTaskRunner> concurrent_task_runner,
+        std::shared_future<impeller::RuntimeStageBackend> runtime_stage_backend,
+        bool enable_impeller,
+        bool enable_flutter_gpu);
 
     /// The task runners used by the shell hosting this runtime controller. This
     /// may be used by the isolate to scheduled asynchronous texture uploads or
@@ -101,14 +104,14 @@ class UIDartState : public tonic::DartState {
     /// of shared worker threads.
     std::shared_ptr<fml::ConcurrentTaskRunner> concurrent_task_runner;
 
+    /// The runtime stage backend for fragment shaders.
+    std::shared_future<impeller::RuntimeStageBackend> runtime_stage_backend;
+
     /// Whether Impeller is enabled or not.
     bool enable_impeller = false;
 
     /// Whether flutter_gpu is enabled or not.
     bool enable_flutter_gpu = false;
-
-    /// The expected backend for runtime stage shaders.
-    impeller::RuntimeStageBackend runtime_stage_backend;
   };
 
   Dart_Port main_port() const { return main_port_; }
@@ -180,7 +183,7 @@ class UIDartState : public tonic::DartState {
   /// Whether Flutter GPU is enabled for this application.
   bool IsFlutterGPUEnabled() const;
 
-  /// The expected type for runtime stage shaders.
+  /// The runtime stage to use for fragment shaders.
   impeller::RuntimeStageBackend GetRuntimeStageBackend() const;
 
   virtual Dart_Isolate CreatePlatformIsolate(Dart_Handle entry_point,

engine/src/flutter/lib/ui/ui_dart_state.h

@@ -60,19 +60,21 @@ std::unique_ptr<RuntimeController> RuntimeController::Spawn(
     fml::TaskRunnerAffineWeakPtr<ImageGeneratorRegistry>
         image_generator_registry,
     fml::TaskRunnerAffineWeakPtr<SnapshotDelegate> snapshot_delegate) const {
-  UIDartState::Context spawned_context{context_.task_runners,
-                                       std::move(snapshot_delegate),
-                                       std::move(io_manager),
-                                       context_.unref_queue,
-                                       std::move(image_decoder),
-                                       std::move(image_generator_registry),
-                                       advisory_script_uri,
-                                       advisory_script_entrypoint,
-                                       context_.deterministic_rendering_enabled,
-                                       context_.concurrent_task_runner,
-                                       context_.enable_impeller,
-                                       context_.enable_flutter_gpu,
-                                       context_.runtime_stage_backend};
+  UIDartState::Context spawned_context{
+      context_.task_runners,
+      std::move(snapshot_delegate),
+      std::move(io_manager),
+      context_.unref_queue,
+      std::move(image_decoder),
+      std::move(image_generator_registry),
+      advisory_script_uri,
+      advisory_script_entrypoint,
+      context_.deterministic_rendering_enabled,
+      context_.concurrent_task_runner,
+      context_.runtime_stage_backend,
+      context_.enable_impeller,
+      context_.enable_flutter_gpu,
+  };
   auto result =
       std::make_unique<RuntimeController>(p_client,                      //
                                           vm_,                           //