安卓平台Flutter启动过程全解析 #2

void FlutterMain::Init(JNIEnv* env,
                       jclass clazz,
                       jobject context,
                       jobjectArray jargs,
                       jstring bundlePath,
                       jstring appStoragePath,
                       jstring engineCachesPath) {
  std::vector<std::string> args;
  args.push_back("flutter");
  for (auto& arg : fml::jni::StringArrayToVector(env, jargs)) {
    args.push_back(std::move(arg));
  }
  auto command_line = fml::CommandLineFromIterators(args.begin(), args.end());

  auto settings = SettingsFromCommandLine(command_line);

  settings.assets_path = fml::jni::JavaStringToString(env, bundlePath);
  ...
  settings.task_observer_add = [](intptr_t key, fml::closure callback) {
    fml::MessageLoop::GetCurrent().AddTaskObserver(key, std::move(callback));
  };

  settings.task_observer_remove = [](intptr_t key) {
    fml::MessageLoop::GetCurrent().RemoveTaskObserver(key);
  };
  ...
  g_flutter_main.reset(new FlutterMain(std::move(settings)));
}

static jlong AttachJNI(JNIEnv* env,
                       jclass clazz,
                       jobject flutterJNI,
                       jboolean is_background_view) {
  fml::jni::JavaObjectWeakGlobalRef java_object(env, flutterJNI);
  auto shell_holder = std::make_unique<AndroidShellHolder>(
      FlutterMain::Get().GetSettings(), java_object, is_background_view);
  if (shell_holder->IsValid()) {
    return reinterpret_cast<jlong>(shell_holder.release());
  } else {
    return 0;
  }
}

//shell/platform/android/android_shell_holder.cc
AndroidShellHolder::AndroidShellHolder(
    blink::Settings settings,
    fml::jni::JavaObjectWeakGlobalRef java_object,
    bool is_background_view)
    : settings_(std::move(settings)), java_object_(java_object) {
  ...
  auto jni_exit_task([key = thread_destruct_key_]() {
    FML_CHECK(pthread_setspecific(key, reinterpret_cast<void*>(1)) == 0);
  });
  thread_host_.ui_thread->GetTaskRunner()->PostTask(jni_exit_task);
  if (!is_background_view) {
    thread_host_.gpu_thread->GetTaskRunner()->PostTask(jni_exit_task);
  }
  ...
  fml::MessageLoop::EnsureInitializedForCurrentThread();
  fml::RefPtr<fml::TaskRunner> gpu_runner;
  fml::RefPtr<fml::TaskRunner> ui_runner;
  fml::RefPtr<fml::TaskRunner> io_runner;
  fml::RefPtr<fml::TaskRunner> platform_runner =
      fml::MessageLoop::GetCurrent().GetTaskRunner();
  if (is_background_view) {
    auto single_task_runner = thread_host_.ui_thread->GetTaskRunner();
    gpu_runner = single_task_runner;
    ui_runner = single_task_runner;
    io_runner = single_task_runner;
  } else {
    gpu_runner = thread_host_.gpu_thread->GetTaskRunner();
    ui_runner = thread_host_.ui_thread->GetTaskRunner();
    io_runner = thread_host_.io_thread->GetTaskRunner();
  }
  blink::TaskRunners task_runners(thread_label,     // label
                                  platform_runner,  // platform
                                  gpu_runner,       // gpu
                                  ui_runner,        // ui
                                  io_runner         // io
  );
  shell_ =
      Shell::Create(task_runners,             // task runners
                    settings_,                // settings
                    on_create_platform_view,  // platform view create callback
                    on_create_rasterizer      // rasterizer create callback
      );
     ...
}

std::unique_ptr<Shell> Shell::Create(
    blink::TaskRunners task_runners,
    blink::Settings settings,
    Shell::CreateCallback<PlatformView> on_create_platform_view,
    Shell::CreateCallback<Rasterizer> on_create_rasterizer) {
   PerformInitializationTasks(settings);
  auto vm = blink::DartVM::ForProcess(settings);
  FML_CHECK(vm) << "Must be able to initialize the VM.";
  return Shell::Create(std::move(task_runners),             //
                       std::move(settings),                 //
                       vm->GetIsolateSnapshot(),            //
                       blink::DartSnapshot::Empty(),        //
                       std::move(on_create_platform_view),  //
                       std::move(on_create_rasterizer)      //
  );
}

  {
          .name = "nativeRunBundleAndSnapshotFromLibrary",
          .signature = "(J[Ljava/lang/String;Ljava/lang/String;"
                       "Ljava/lang/String;Landroid/content/res/AssetManager;)V",
          .fnPtr =
              reinterpret_cast<void*>(&shell::RunBundleAndSnapshotFromLibrary),
 }

static void RunBundleAndSnapshotFromLibrary(JNIEnv* env,
                                            jobject jcaller,
                                            jlong shell_holder,
                                            jobjectArray jbundlepaths,
                                            jstring jEntrypoint,
                                            jstring jLibraryUrl,
                                            jobject jAssetManager) {
  auto asset_manager = std::make_shared<blink::AssetManager>();
  for (const auto& bundlepath :
       fml::jni::StringArrayToVector(env, jbundlepaths)) {
    ...
    const auto file_ext_index = bundlepath.rfind(".");
    if (bundlepath.substr(file_ext_index) == ".zip") {
        //资源解压
      asset_manager->PushBack(std::make_unique<blink::ZipAssetStore>(
          bundlepath, "assets/flutter_assets"));

    } else {
      //操作资源地址并存储到容器中
      asset_manager->PushBack(
          std::make_unique<blink::DirectoryAssetBundle>(fml::OpenDirectory(
              bundlepath.c_str(), false, fml::FilePermission::kRead)));
      ...
    }
  }

  auto isolate_configuration = CreateIsolateConfiguration(*asset_manager);
  ...
  RunConfiguration config(std::move(isolate_configuration),
                          std::move(asset_manager));

  {
    auto entrypoint = fml::jni::JavaStringToString(env, jEntrypoint);
    auto libraryUrl = fml::jni::JavaStringToString(env, jLibraryUrl);

    if ((entrypoint.size() > 0) && (libraryUrl.size() > 0)) {
        //设置dart的入口函数，entrypoint为“main”，引用库地址
      config.SetEntrypointAndLibrary(std::move(entrypoint),
                                     std::move(libraryUrl));
    } else if (entrypoint.size() > 0) {
      config.SetEntrypoint(std::move(entrypoint));
    }
  }

  ANDROID_SHELL_HOLDER->Launch(std::move(config));
}

void AndroidShellHolder::Launch(RunConfiguration config) {
  //is_valid_ = shell_ != nullptr;正常情况下为true
  if (!IsValid()) {
    return;
  }

  shell_->GetTaskRunners().GetUITaskRunner()->PostTask(
      fml::MakeCopyable([engine = shell_->GetEngine(),  //拿到了引擎的弱引用对象
                         config = std::move(config)     
  ]() mutable {
        ...
        //next
        if (!engine || engine->Run(std::move(config)) ==
                           shell::Engine::RunStatus::Failure) {
        ...
        }
        ...
      }));
}

//engine.cc
Engine::RunStatus Engine::Run(RunConfiguration configuration) {
  ...
  auto isolate_launch_status =
      PrepareAndLaunchIsolate(std::move(configuration));
  ....
}

shell::Engine::RunStatus Engine::PrepareAndLaunchIsolate(
    RunConfiguration configuration) {
  TRACE_EVENT0("flutter", "Engine::PrepareAndLaunchIsolate");
  UpdateAssetManager(configuration.GetAssetManager());
  auto isolate_configuration = configuration.TakeIsolateConfiguration();
  std::shared_ptr<blink::DartIsolate> isolate =
      runtime_controller_->GetRootIsolate().lock();

  if (!isolate) {
    return RunStatus::Failure;
  }
  ...
  if (!isolate_configuration->PrepareIsolate(*isolate)) {
    FML_LOG(ERROR) << "Could not prepare to run the isolate.";
    return RunStatus::Failure;
  }
  if (configuration.GetEntrypointLibrary().empty()) {
    if (!isolate->Run(configuration.GetEntrypoint())) {
      FML_LOG(ERROR) << "Could not run the isolate.";
      return RunStatus::Failure;
    }
  } else {
    if (!isolate->RunFromLibrary(configuration.GetEntrypointLibrary(),
                                 configuration.GetEntrypoint())) {
      FML_LOG(ERROR) << "Could not run the isolate.";
      return RunStatus::Failure;
    }
  }

  return RunStatus::Success;
}

//dart_api_impl.cc
FML_WARN_UNUSED_RESULT
bool DartIsolate::Run(const std::string& entrypoint_name) {
 ...   
  auto user_entrypoint_function =
      Dart_GetField(Dart_RootLibrary(), tonic::ToDart(entrypoint_name.c_str()));
  if (!InvokeMainEntrypoint(user_entrypoint_function)) {
    return false;
  }
 ...
}

//dart_isolate.cc
FML_WARN_UNUSED_RESULT
static bool InvokeMainEntrypoint(Dart_Handle user_entrypoint_function) {
  ...
  Dart_Handle start_main_isolate_function =
      tonic::DartInvokeField(Dart_LookupLibrary(tonic::ToDart("dart:isolate")),
                             "_getStartMainIsolateFunction", {});
  ...
  if (tonic::LogIfError(tonic::DartInvokeField(
          Dart_LookupLibrary(tonic::ToDart("dart:ui")), "_runMainZoned",
          {start_main_isolate_function, user_entrypoint_function}))) {
    FML_LOG(ERROR) << "Could not invoke the main entrypoint.";
    return false;
  }
  return true;
}

DART_EXPORT Dart_Handle Dart_Invoke(Dart_Handle target,
                                    Dart_Handle name,
                                    int number_of_arguments,
                                    Dart_Handle* arguments) {                               
  DARTSCOPE(Thread::Current());
  API_TIMELINE_DURATION(T);
  CHECK_CALLBACK_STATE(T);
  String& function_name =
      String::Handle(Z, Api::UnwrapStringHandle(Z, name).raw());
  if (function_name.IsNull()) {
    RETURN_TYPE_ERROR(Z, name, String);
  }
  if (number_of_arguments < 0) {
    return Api::NewError(
        "%s expects argument 'number_of_arguments' to be non-negative.",
        CURRENT_FUNC);
  }
  ...
  if (obj.IsType()) {
    ...
    const Class& cls = Class::Handle(Z, Type::Cast(obj).type_class());
    ...
    //分析节点1
    return Api::NewHandle(
        T, cls.Invoke(function_name, args, arg_names, respect_reflectable,
                      check_is_entrypoint));
  } else if (obj.IsNull() || obj.IsInstance()) {
     ...
    Instance& instance = Instance::Handle(Z);
    ...
    //分析节点2
    return Api::NewHandle(
        T, instance.Invoke(function_name, args, arg_names, respect_reflectable,
                           check_is_entrypoint));
  } else if (obj.IsLibrary()) {
    ...
    const Library& lib = Library::Cast(obj);
    ...
    //分析节点3
    return Api::NewHandle(
        T, lib.Invoke(function_name, args, arg_names, respect_reflectable,
                      check_is_entrypoint));
  } 
  ...
}

//object.cc
RawObject* Library::Invoke(const String& function_name,
                           const Array& args,
                           const Array& arg_names,
                           bool respect_reflectable,
                           bool check_is_entrypoint) const {
    ...
    Function& function = Function::Handle(zone, LookupStaticFunction(function_name));
    ...
    return DartEntry::InvokeFunction(function, args, args_descriptor_array);  
    ...
}

RawObject* DartEntry::InvokeFunction(const Function& function,
                                     const Array& arguments,
                                     const Array& arguments_descriptor,
                                     uword current_sp) {
...
#if defined(TARGET_ARCH_DBC)
  //具体方法解析调用
  return Simulator::Current()->Call(code, arguments_descriptor, arguments,
                                    thread);
#elif defined(USING_SIMULATOR)
 //模拟器
  return bit_copy<RawObject*, int64_t>(Simulator::Current()->Call(
      reinterpret_cast<intptr_t>(entrypoint), reinterpret_cast<intptr_t>(&code),
      reinterpret_cast<intptr_t>(&arguments_descriptor),
      reinterpret_cast<intptr_t>(&arguments),
      reinterpret_cast<intptr_t>(thread)));
      ...
}