Implemented FlutterEngineGroup and Spawn API.

ci/licenses_golden/licenses_flutter

@@ -945,6 +945,7 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterAppDel
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterCallbackCache.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterDartProject.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngine.h
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngineGroup.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterHeadlessDartRunner.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlatformViews.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Headers/FlutterPlugin.h
@@ -963,6 +964,8 @@ FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterDartPro
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProjectTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEngineGroup.mm
+FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEngineGroupTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEngineTest.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h

shell/common/shell.cc

@@ -436,6 +436,21 @@ Shell::~Shell() {
   platform_latch.Wait();
 }
 
+std::unique_ptr<Shell> Shell::Spawn(
+    Settings settings,
+    const CreateCallback<PlatformView>& on_create_platform_view,
+    const CreateCallback<Rasterizer>& on_create_rasterizer) {
+  RunConfiguration configuration =
+      RunConfiguration::InferFromSettings(settings);
+  TaskRunners task_runners = task_runners_;
+  FML_DCHECK(task_runners.IsValid());
+  std::unique_ptr<Shell> result(Shell::Create(std::move(task_runners), settings,
+                                              on_create_platform_view,
+                                              on_create_rasterizer));
+  result->RunEngine(std::move(configuration));
+  return result;
+}
+
 void Shell::NotifyLowMemoryWarning() const {
   auto trace_id = fml::tracing::TraceNonce();
   TRACE_EVENT_ASYNC_BEGIN0("flutter", "Shell::NotifyLowMemoryWarning",

shell/common/shell.h

@@ -220,6 +220,19 @@ class Shell final : public PlatformView::Delegate,
   ///
   ~Shell();
 
+  //----------------------------------------------------------------------------
+  /// @brief      Creates one Shell from another Shell where the created Shell
+  ///             takes the opportunity to share any internal components it can.
+  ///             This results is a Shell that has a smaller startup time cost
+  ///             and a smaller memory footprint than an Shell created with a
+  ///             Create function.
+  ///
+  /// @see        http://flutter.dev/go/multiple-engines
+  std::unique_ptr<Shell> Spawn(
+      Settings settings,
+      const CreateCallback<PlatformView>& on_create_platform_view,
+      const CreateCallback<Rasterizer>& on_create_rasterizer);
+
   //----------------------------------------------------------------------------
   /// @brief      Starts an isolate for the given RunConfiguration.
   ///

shell/common/shell_unittests.cc

@@ -32,6 +32,7 @@
 #include "flutter/shell/common/vsync_waiter_fallback.h"
 #include "flutter/shell/version/version.h"
 #include "flutter/testing/testing.h"
+#include "gmock/gmock.h"
 #include "third_party/rapidjson/include/rapidjson/writer.h"
 #include "third_party/skia/include/core/SkPictureRecorder.h"
 #include "third_party/tonic/converter/dart_converter.h"
@@ -42,6 +43,77 @@
 
 namespace flutter {
 namespace testing {
+namespace {
+class MockPlatformViewDelegate : public PlatformView::Delegate {
+  MOCK_METHOD1(OnPlatformViewCreated, void(std::unique_ptr<Surface> surface));
+
+  MOCK_METHOD0(OnPlatformViewDestroyed, void());
+
+  MOCK_METHOD1(OnPlatformViewSetNextFrameCallback,
+               void(const fml::closure& closure));
+
+  MOCK_METHOD1(OnPlatformViewSetViewportMetrics,
+               void(const ViewportMetrics& metrics));
+
+  MOCK_METHOD1(OnPlatformViewDispatchPlatformMessage,
+               void(fml::RefPtr<PlatformMessage> message));
+
+  MOCK_METHOD1(OnPlatformViewDispatchPointerDataPacket,
+               void(std::unique_ptr<PointerDataPacket> packet));
+
+  MOCK_METHOD3(OnPlatformViewDispatchSemanticsAction,
+               void(int32_t id,
+                    SemanticsAction action,
+                    std::vector<uint8_t> args));
+
+  MOCK_METHOD1(OnPlatformViewSetSemanticsEnabled, void(bool enabled));
+
+  MOCK_METHOD1(OnPlatformViewSetAccessibilityFeatures, void(int32_t flags));
+
+  MOCK_METHOD1(OnPlatformViewRegisterTexture,
+               void(std::shared_ptr<Texture> texture));
+
+  MOCK_METHOD1(OnPlatformViewUnregisterTexture, void(int64_t texture_id));
+
+  MOCK_METHOD1(OnPlatformViewMarkTextureFrameAvailable,
+               void(int64_t texture_id));
+
+  MOCK_METHOD3(LoadDartDeferredLibrary,
+               void(intptr_t loading_unit_id,
+                    std::unique_ptr<const fml::Mapping> snapshot_data,
+                    std::unique_ptr<const fml::Mapping> snapshot_instructions));
+
+  MOCK_METHOD3(LoadDartDeferredLibraryError,
+               void(intptr_t loading_unit_id,
+                    const std::string error_message,
+                    bool transient));
+
+  MOCK_METHOD1(UpdateAssetManager,
+               void(std::shared_ptr<AssetManager> asset_manager));
+};
+
+class MockSurface : public Surface {
+  MOCK_METHOD0(IsValid, bool());
+
+  MOCK_METHOD1(AcquireFrame,
+               std::unique_ptr<SurfaceFrame>(const SkISize& size));
+
+  MOCK_CONST_METHOD0(GetRootTransformation, SkMatrix());
+
+  MOCK_METHOD0(GetContext, GrDirectContext*());
+
+  MOCK_METHOD0(MakeRenderContextCurrent, std::unique_ptr<GLContextResult>());
+
+  MOCK_METHOD0(ClearRenderContext, bool());
+};
+
+class MockPlatformView : public PlatformView {
+ public:
+  MockPlatformView(MockPlatformViewDelegate& delegate, TaskRunners task_runners)
+      : PlatformView(delegate, task_runners) {}
+  MOCK_METHOD0(CreateRenderingSurface, std::unique_ptr<Surface>());
+};
+}  // namespace
 
 static bool ValidateShell(Shell* shell) {
   if (!shell) {
@@ -2318,5 +2390,52 @@ TEST_F(ShellTest, AssetManagerMulti) {
   }
 }
 
+TEST_F(ShellTest, Spawn) {
+  auto settings = CreateSettingsForFixture();
+  auto shell = CreateShell(settings);
+  ASSERT_TRUE(ValidateShell(shell.get()));
+
+  auto configuration = RunConfiguration::InferFromSettings(settings);
+  ASSERT_TRUE(configuration.IsValid());
+  configuration.SetEntrypoint("fixturesAreFunctionalMain");
+
+  fml::AutoResetWaitableEvent main_latch;
+  AddNativeCallback(
+      "SayHiFromFixturesAreFunctionalMain",
+      CREATE_NATIVE_ENTRY([&main_latch](auto args) { main_latch.Signal(); }));
+
+  RunEngine(shell.get(), std::move(configuration));
+  main_latch.Wait();
+  ASSERT_TRUE(DartVMRef::IsInstanceRunning());
+
+  {
+    fml::AutoResetWaitableEvent latch;
+    fml::TaskRunner::RunNowOrPostTask(
+        shell->GetTaskRunners().GetPlatformTaskRunner(),
+        [this, &spawner = shell, &latch, settings]() {
+          MockPlatformViewDelegate platform_view_delegate;
+          auto spawn = spawner->Spawn(
+              settings,
+              [&platform_view_delegate](Shell& shell) {
+                auto result = std::make_unique<MockPlatformView>(
+                    platform_view_delegate, shell.GetTaskRunners());
+                ON_CALL(*result, CreateRenderingSurface())
+                    .WillByDefault(::testing::Invoke(
+                        [] { return std::make_unique<MockSurface>(); }));
+                return result;
+              },
+              [](Shell& shell) { return std::make_unique<Rasterizer>(shell); });
+          ASSERT_NE(nullptr, spawn.get());
+          ASSERT_TRUE(ValidateShell(spawn.get()));
+          DestroyShell(std::move(spawn));
+          latch.Signal();
+        });
+    latch.Wait();
+  }
+
+  DestroyShell(std::move(shell));
+  ASSERT_FALSE(DartVMRef::IsInstanceRunning());
+}
+
 }  // namespace testing
 }  // namespace flutter

shell/platform/darwin/ios/BUILD.gn

@@ -28,6 +28,7 @@ _flutter_framework_headers = [
   "framework/Headers/FlutterCallbackCache.h",
   "framework/Headers/FlutterDartProject.h",
   "framework/Headers/FlutterEngine.h",
+  "framework/Headers/FlutterEngineGroup.h",
   "framework/Headers/FlutterHeadlessDartRunner.h",
   "framework/Headers/FlutterPlatformViews.h",
   "framework/Headers/FlutterPlugin.h",
@@ -52,6 +53,7 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterDartProject.mm",
     "framework/Source/FlutterDartProject_Internal.h",
     "framework/Source/FlutterEngine.mm",
+    "framework/Source/FlutterEngineGroup.mm",
     "framework/Source/FlutterEngine_Internal.h",
     "framework/Source/FlutterHeadlessDartRunner.mm",
     "framework/Source/FlutterObservatoryPublisher.h",
@@ -215,6 +217,7 @@ shared_library("ios_test_flutter") {
     "framework/Source/FlutterAppDelegateTest.mm",
     "framework/Source/FlutterBinaryMessengerRelayTest.mm",
     "framework/Source/FlutterDartProjectTest.mm",
+    "framework/Source/FlutterEngineGroupTest.mm",
     "framework/Source/FlutterEngineTest.mm",
     "framework/Source/FlutterPluginAppLifeCycleDelegateTest.m",
     "framework/Source/FlutterTextInputPluginTest.m",

shell/platform/darwin/ios/framework/Headers/Flutter.h

@@ -12,6 +12,7 @@
 #import "FlutterCodecs.h"
 #import "FlutterDartProject.h"
 #import "FlutterEngine.h"
+#import "FlutterEngineGroup.h"
 #import "FlutterHeadlessDartRunner.h"
 #import "FlutterMacros.h"
 #import "FlutterPlatformViews.h"

shell/platform/darwin/ios/framework/Headers/FlutterEngineGroup.h

@@ -0,0 +1,45 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Foundation/Foundation.h>
+
+#import "FlutterEngine.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+/**
+ * Represents a collection of FlutterEngines who share resources which allows
+ * them to be created with less time const and occupy less memory than just
+ * creating multiple FlutterEngines.
+ *
+ * Deleting a FlutterEngineGroup doesn't invalidate existing FlutterEngines, but
+ * it eliminates the possibility to create more FlutterEngines in that group.
+ *
+ * @warning This class is a work-in-progress and may change.
+ * @see https://github.com/flutter/flutter/issues/72009
+ */
+@interface FlutterEngineGroup : NSObject
+- (instancetype)init NS_UNAVAILABLE;
+
+/**
+ * Initialize a new FlutterEngineGroup.
+ *
+ * @param name The name that will present in the threads shared across the
+ * engines in this group.
+ * @param project The `FlutterDartProject` that all FlutterEngines in this group
+ * will be executing.
+ */
+- (instancetype)initWithName:(NSString*)name
+                     project:(nullable FlutterDartProject*)project NS_DESIGNATED_INITIALIZER;
+
+/**
+ * Creates a running `FlutterEngine` that shares components with this group.
+ *
+ * @see FlutterEngineGroup
+ */
+- (FlutterEngine*)makeEngineWithEntrypoint:(nullable NSString*)entrypoint
+                                libraryURI:(nullable NSString*)libraryURI;
+@end
+
+NS_ASSUME_NONNULL_END