flutter::Engine Class Reference

#include <engine.h>

Inheritance diagram for flutter::Engine:

Classes
class	Delegate
	While the engine operates entirely on the UI task runner, it needs the capabilities of the other components to fulfill the requirements of the root isolate. The shell is the only class that implements this interface as no other component has access to all components in a thread safe manner. The engine delegates these tasks to the shell via this interface. More...

Public Types
enum class	RunStatus { Success , FailureAlreadyRunning , Failure }
	Indicates the result of the call to Engine::Run. More...

Public Member Functions
	Engine (Delegate &delegate, const PointerDataDispatcherMaker &dispatcher_maker, const std::shared_ptr< fml::ConcurrentTaskRunner > &image_decoder_task_runner, const TaskRunners &task_runners, const Settings &settings, std::unique_ptr< Animator > animator, const fml::WeakPtr< IOManager > &io_manager, const std::shared_ptr< FontCollection > &font_collection, std::unique_ptr< RuntimeController > runtime_controller, const std::shared_ptr< fml::SyncSwitch > &gpu_disabled_switch)
	Creates an instance of the engine with a supplied RuntimeController. Use the other constructor except for tests. More...
	Engine (Delegate &delegate, const PointerDataDispatcherMaker &dispatcher_maker, DartVM &vm, fml::RefPtr< const DartSnapshot > isolate_snapshot, const TaskRunners &task_runners, const PlatformData &platform_data, const Settings &settings, std::unique_ptr< Animator > animator, fml::WeakPtr< IOManager > io_manager, const fml::RefPtr< SkiaUnrefQueue > &unref_queue, fml::TaskRunnerAffineWeakPtr< SnapshotDelegate > snapshot_delegate, std::shared_ptr< VolatilePathTracker > volatile_path_tracker, const std::shared_ptr< fml::SyncSwitch > &gpu_disabled_switch, impeller::RuntimeStageBackend runtime_stage_type=impeller::RuntimeStageBackend::kSkSL)
	Creates an instance of the engine. This is done by the Shell on the UI task runner. More...
std::unique_ptr< Engine >	Spawn (Delegate &delegate, const PointerDataDispatcherMaker &dispatcher_maker, const Settings &settings, std::unique_ptr< Animator > animator, const std::string &initial_route, const fml::WeakPtr< IOManager > &io_manager, fml::TaskRunnerAffineWeakPtr< SnapshotDelegate > snapshot_delegate, const std::shared_ptr< fml::SyncSwitch > &gpu_disabled_switch) const
	Create a Engine that shares as many resources as possible with the calling Engine such that together they occupy less memory and be created faster. More...
	~Engine () override
	Destroys the engine engine. Called by the shell on the UI task runner. The running root isolate is terminated and will no longer access the task runner after this call returns. This allows the embedder to tear down the thread immediately if needed. More...
fml::WeakPtr< Engine >	GetWeakPtr () const
RunStatus	Run (RunConfiguration configuration)
	Moves the root isolate to the DartIsolate::Phase::Running phase on a successful call to this method. More...
bool	Restart (RunConfiguration configuration)
	Tears down an existing root isolate, reuses the components of that isolate and attempts to launch a new isolate using the given the run configuration. This is only used in the "debug" Flutter runtime mode in the cold-restart scenario. More...
void	SetupDefaultFontManager ()
	Setup default font manager according to specific platform. More...
bool	UpdateAssetManager (const std::shared_ptr< AssetManager > &asset_manager)
	Updates the asset manager referenced by the root isolate of a Flutter application. This happens implicitly in the call to Engine::Run and Engine::Restart as the asset manager is referenced from the run configuration provided to those calls. In addition to the Engine::Run and Engine::Restart calls, the tooling may need to update the assets available to the application as the user adds them to their project. For example, these assets may be referenced by code that is newly patched in after a hot-reload. Neither the shell or the isolate in relaunched in such cases. The tooling usually patches in the new assets in a temporary location and updates the asset manager to point to that location. More...
void	BeginFrame (fml::TimePoint frame_time, uint64_t frame_number)
	Notifies the engine that it is time to begin working on a new frame previously scheduled via a call to Engine::ScheduleFrame. This call originates in the animator. More...
void	NotifyIdle (fml::TimeDelta deadline)
	Notifies the engine that the UI task runner is not expected to undertake a new frame workload till a specified timepoint. The timepoint is measured in microseconds against the system's monotonic clock. It is recommended that the clock be accessed via Dart_TimelineGetMicros from dart_api.h for consistency. In reality, the clocks used by Dart, FML and std::steady_clock are all the same and the timepoints can be converted from on clock type to another. More...
void	NotifyDestroyed ()
	Notifies the engine that the attached flutter view has been destroyed. This enables the engine to notify the Dart VM so it can do some cleanp activities. More...
void	ReportTimings (std::vector< int64_t > timings)
	Dart code cannot fully measure the time it takes for a specific frame to be rendered. This is because Dart code only runs on the UI task runner. That is only a small part of the overall frame workload. The raster task runner frame workload is executed on a thread where Dart code cannot run (and hence instrument). Besides, due to the pipelined nature of rendering in Flutter, there may be multiple frame workloads being processed at any given time. However, for non-Timeline based profiling, it is useful for trace collection and processing to happen in Dart. To do this, the raster task runner frame workloads need to be instrumented separately. After a set number of these profiles have been gathered, they need to be reported back to Dart code. The shell reports this extra instrumentation information back to Dart code running on the engine by invoking this method at predefined intervals. More...
Dart_Port	GetUIIsolateMainPort ()
	Gets the main port of the root isolate. Since the isolate is created immediately in the constructor of the engine, it is possible to get its main port immediately (even before a call to Run can be made). This is useful in registering the port in a race free manner with a port nameserver. More...
std::string	GetUIIsolateName ()
	Gets the debug name of the root isolate. By default, the debug name of the isolate is derived from its advisory script URI, advisory main entrypoint and its main port name. For example, "main.dart$main-1234" where the script URI is "main.dart", the entrypoint is "main" and the port name "1234". Once launched, the isolate may re-christen itself using a name it selects via setIsolateDebugName in platform_dispatcher.dart. This name is purely advisory and only used by instrumentation and reporting purposes. More...
bool	UIIsolateHasLivePorts ()
	It is an unexpected challenge to determine when a Dart application is "done". The application cannot simply terminate the native process (and perhaps return an exit code) because it does not have that power. After all, Flutter applications reside within a host process that may have other responsibilities besides just running Flutter applications. Also, the main entry-points are run on an event loop and returning from "main" (unlike in C/C++ applications) does not mean termination of the process. Besides, the return value of the main entrypoint is discarded. More...
tonic::DartErrorHandleType	GetUIIsolateLastError ()
	Errors that are unhandled on the Dart message loop are kept for further inspection till the next unhandled error comes along. This accessor returns the last unhandled error encountered by the root isolate. More...
std::optional< uint32_t >	GetUIIsolateReturnCode ()
	As described in the discussion for UIIsolateHasLivePorts, the "done-ness" of a Dart application is tricky to ascertain and the return value from the main entrypoint is discarded (because the Dart isolate is still running after the main entrypoint returns). But, the concept of an exit code akin to those returned by native applications is still useful. Short lived Dart applications (usually tests), emulate this by setting a per isolate "return value" and then indicating their "done-ness" (usually via closing all live ports). This accessor returns that "return value" is present. More...
void	AddView (int64_t view_id, const ViewportMetrics &view_metrics, std::function< void(bool added)> callback)
	Notify the Flutter application that a new view is available. More...
bool	RemoveView (int64_t view_id)
	Notify the Flutter application that a view is no longer available. More...
void	SetViewportMetrics (int64_t view_id, const ViewportMetrics &metrics)
	Updates the viewport metrics for a view. The viewport metrics detail the size of the rendering viewport in texels as well as edge insets if present. More...
void	SetDisplays (const std::vector< DisplayData > &displays)
	Updates the display metrics for the currently running Flutter application. More...
void	DispatchPlatformMessage (std::unique_ptr< PlatformMessage > message)
	Notifies the engine that the embedder has sent it a message. This call originates in the platform view and has been forwarded to the engine on the UI task runner here. More...
void	DispatchPointerDataPacket (std::unique_ptr< PointerDataPacket > packet, uint64_t trace_flow_id)
	Notifies the engine that the embedder has sent it a pointer data packet. A pointer data packet may contain multiple input events. This call originates in the platform view and the shell has forwarded the same to the engine on the UI task runner here. More...
void	DispatchSemanticsAction (int node_id, SemanticsAction action, fml::MallocMapping args)
	Notifies the engine that the embedder encountered an accessibility related action on the specified node. This call originates on the platform view and has been forwarded to the engine here on the UI task runner by the shell. More...
void	SetSemanticsEnabled (bool enabled)
	Notifies the engine that the embedder has expressed an opinion about whether the accessibility tree should be generated or not. This call originates in the platform view and is forwarded to the engine here on the UI task runner by the shell. More...
void	SetAccessibilityFeatures (int32_t flags)
	Notifies the engine that the embedder has expressed an opinion about where the flags to set on the accessibility tree. This flag originates in the platform view and is forwarded to the engine here on the UI task runner by the shell. More...
void	ScheduleFrame (bool regenerate_layer_trees) override
void	ScheduleFrame ()
void	OnAllViewsRendered () override
FontCollection &	GetFontCollection () override
std::shared_ptr< AssetManager >	GetAssetManager () override
fml::WeakPtr< ImageDecoder >	GetImageDecoderWeakPtr ()
fml::WeakPtr< ImageGeneratorRegistry >	GetImageGeneratorRegistry ()
	Get the ImageGeneratorRegistry associated with the current engine. More...
void	DoDispatchPacket (std::unique_ptr< PointerDataPacket > packet, uint64_t trace_flow_id) override
void	ScheduleSecondaryVsyncCallback (uintptr_t id, const fml::closure &callback) override
	Schedule a secondary callback to be executed right after the main VsyncWaiter::AsyncWaitForVsync callback (which is added by Animator::RequestFrame). More...
const std::string &	GetLastEntrypoint () const
	Get the last Entrypoint that was used in the RunConfiguration when |Engine::Run| was called. More...
const std::string &	GetLastEntrypointLibrary () const
	Get the last Entrypoint Library that was used in the RunConfiguration when |Engine::Run| was called. More...
const std::vector< std::string > &	GetLastEntrypointArgs () const
	Get the last Entrypoint Arguments that was used in the RunConfiguration when |Engine::Run| was called.This is only valid in debug mode. More...
const std::string &	InitialRoute () const
	Getter for the initial route. This can be set with a platform message. More...
void	LoadDartDeferredLibrary (intptr_t loading_unit_id, std::unique_ptr< const fml::Mapping > snapshot_data, std::unique_ptr< const fml::Mapping > snapshot_instructions)
	Loads the Dart shared library into the Dart VM. When the Dart library is loaded successfully, the Dart future returned by the originating loadLibrary() call completes. More...
void	LoadDartDeferredLibraryError (intptr_t loading_unit_id, const std::string &error_message, bool transient)
	Indicates to the dart VM that the request to load a deferred library with the specified loading unit id has failed. More...
const RuntimeController *	GetRuntimeController () const
	Accessor for the RuntimeController. More...
const std::weak_ptr< VsyncWaiter >	GetVsyncWaiter () const
void	ShutdownPlatformIsolates ()
	Shuts down all registered platform isolates. Must be called from the platform thread. More...
virtual std::string	DefaultRouteName ()=0
virtual void	ScheduleFrame (bool regenerate_layer_trees=true)=0
virtual void	OnAllViewsRendered ()=0
virtual void	Render (int64_t view_id, std::unique_ptr< flutter::LayerTree > layer_tree, float device_pixel_ratio)=0
virtual void	UpdateSemantics (SemanticsNodeUpdates update, CustomAccessibilityActionUpdates actions)=0
virtual void	HandlePlatformMessage (std::unique_ptr< PlatformMessage > message)=0
virtual FontCollection &	GetFontCollection ()=0
virtual std::shared_ptr< AssetManager >	GetAssetManager ()=0
virtual void	OnRootIsolateCreated ()=0
virtual void	UpdateIsolateDescription (const std::string isolate_name, int64_t isolate_port)=0
virtual void	SetNeedsReportTimings (bool value)=0
virtual std::unique_ptr< std::vector< std::string > >	ComputePlatformResolvedLocale (const std::vector< std::string > &supported_locale_data)=0
virtual void	RequestDartDeferredLibrary (intptr_t loading_unit_id)=0
virtual std::weak_ptr< PlatformMessageHandler >	GetPlatformMessageHandler () const =0
virtual void	SendChannelUpdate (std::string name, bool listening)=0
virtual double	GetScaledFontSize (double unscaled_font_size, int configuration_id) const =0

Friends
class	testing::ShellTest

Additional Inherited Members
Protected Member Functions inherited from flutter::RuntimeDelegate
virtual	~RuntimeDelegate ()

Detailed Description

The engine is a component owned by the shell that resides on the UI task runner and is responsible for managing the needs of the root isolate and its runtime. The engine can only be created, accessed and collected on the UI task runner. Each shell owns exactly one instance of the engine.

The root isolate of Flutter application gets "window" bindings. Using these bindings, the application can schedule frames, post layer-trees for rendering, ask to decompress images and upload them to the GPU, etc.. Non-root isolates of the VM do not get any of these capabilities and are run in a VM managed thread pool (so if they did have "window", the threading guarantees needed for engine operation would be violated).

The engine is responsible for the entire life-cycle of the root isolate. When the engine is collected, its owner assumes that the root isolate has been shutdown and appropriate resources collected. While each engine instance can only manage a single instance of a root isolate, it may restart that isolate on request. This is how the cold-restart development scenario is supported.

When the engine instance is initially created, the root isolate is created but it is not in the |DartIsolate::Phase::Running| phase yet. It only moves into that phase when a successful call to Engine::Run is made.

See also

Shell

Note

This name of this class is perhaps a bit unfortunate and has sometimes been the cause of confusion. For a class named "Engine" in the Flutter "Engine" repository, its responsibilities are decidedly unremarkable. But, it does happen to be the primary entry-point used by components higher up in the Flutter tech stack (usually in Dart code) to peer into the lower level functionality. Besides, the authors haven't been able to come up with a more apt name and it does happen to be one of the older classes in the repository.

Definition at line 73 of file engine.h.

Member Enumeration Documentation

RunStatus

enum class flutter::Engine::RunStatus

strong

Indicates the result of the call to Engine::Run.

Enumerator
Success	The call to |Engine::Run| was successful and the root isolate is in the DartIsolate::Phase::Running phase with its entry-point invocation already pending in the task queue.
FailureAlreadyRunning	The engine can only manage a single instance of a root isolate. If a previous call to run the root isolate was successful, subsequent calls to run the isolate (even if the new run configuration is different) will be rejected. It is up to the caller to decide to re-purpose the running isolate, terminate it, or use another shell to host the new isolate. This is mostly used by embedders which have a fire-and-forget strategy to root isolate launch. For example, the application may try to "launch" an isolate when the embedders launches or resumes from a paused state. That the isolate is running is not necessarily a failure condition for them. But from the engine's perspective, the run configuration was rejected.
Failure	Used to indicate to the embedder that a root isolate was not already running but the run configuration was not valid and root isolate could not be moved into the DartIsolate::Phase::Running phase. The caller must attempt the run call again with a valid configuration. The set of all failure modes is massive and can originate from a variety of sub-components. The engine will attempt to log the same when possible. With the aid of logs, the common causes of failure are: AOT assets were given to JIT/DBC mode VM's and vice-versa. The assets could not be found in the asset manager. Callers must make sure their run configuration asset managers have been correctly set up. The assets themselves were corrupt or invalid. Callers must make sure their asset delivery mechanisms are sound. The application entry-point or the root library of the entry-point specified in the run configuration was invalid. Callers must make sure that the entry-point is present in the application. If the name of the entrypoint is not "main" in the root library, callers must also ensure that the snapshotting process has not tree-shaken away this entrypoint. This requires the decoration of the entrypoint with the ‘@pragma('vm:entry-point’)` directive. This problem will manifest in AOT mode operation of the Dart VM.

Definition at line 78 of file engine.h.

                       {
    // NOLINTBEGIN(readability-identifier-naming)
    //--------------------------------------------------------------------------
    /// The call to |Engine::Run| was successful and the root isolate is in the
    /// `DartIsolate::Phase::Running` phase with its entry-point invocation
    /// already pending in the task queue.
    ///
    Success,
 
    //--------------------------------------------------------------------------
    /// The engine can only manage a single instance of a root isolate. If a
    /// previous call to run the root isolate was successful, subsequent calls
    /// to run the isolate (even if the new run configuration is different) will
    /// be rejected.
    ///
    /// It is up to the caller to decide to re-purpose the running isolate,
    /// terminate it, or use another shell to host the new isolate. This is
    /// mostly used by embedders which have a fire-and-forget strategy to root
    /// isolate launch. For example, the application may try to "launch" an
    /// isolate when the embedders launches or resumes from a paused state. That
    /// the isolate is running is not necessarily a failure condition for them.
    /// But from the engine's perspective, the run configuration was rejected.
    ///
    FailureAlreadyRunning,
 
    //--------------------------------------------------------------------------
    /// Used to indicate to the embedder that a root isolate was not already
    /// running but the run configuration was not valid and root isolate could
    /// not be moved into the `DartIsolate::Phase::Running` phase.
    ///
    /// The caller must attempt the run call again with a valid configuration.
    /// The set of all failure modes is massive and can originate from a variety
    /// of sub-components. The engine will attempt to log the same when
    /// possible. With the aid of logs, the common causes of failure are:
    ///
    /// * AOT assets were given to JIT/DBC mode VM's and vice-versa.
    /// * The assets could not be found in the asset manager. Callers must make
    ///   sure their run configuration asset managers have been correctly set
    ///   up.
    /// * The assets themselves were corrupt or invalid. Callers must make sure
    ///   their asset delivery mechanisms are sound.
    /// * The application entry-point or the root library of the entry-point
    ///   specified in the run configuration was invalid. Callers must make sure
    ///   that the entry-point is present in the application. If the name of the
    ///   entrypoint is not "main" in the root library, callers must also ensure
    ///   that the snapshotting process has not tree-shaken away this
    ///   entrypoint. This requires the decoration of the entrypoint with the
    ///   `@pragma('vm:entry-point')` directive. This problem will manifest in
    ///   AOT mode operation of the Dart VM.
    ///
    Failure,
    // NOLINTEND(readability-identifier-naming)
  };

Constructor & Destructor Documentation

Engine() [1/2]

flutter::Engine::Engine	(	Delegate &	delegate,
		const PointerDataDispatcherMaker &	dispatcher_maker,
		const std::shared_ptr< fml::ConcurrentTaskRunner > &	image_decoder_task_runner,
		const TaskRunners &	task_runners,
		const Settings &	settings,
		std::unique_ptr< Animator >	animator,
		const fml::WeakPtr< IOManager > &	io_manager,
		const std::shared_ptr< FontCollection > &	font_collection,
		std::unique_ptr< RuntimeController >	runtime_controller,
		const std::shared_ptr< fml::SyncSwitch > &	gpu_disabled_switch
	)

Creates an instance of the engine with a supplied RuntimeController. Use the other constructor except for tests.

Definition at line 40 of file engine.cc.

    : delegate_(delegate),
      settings_(settings),
      animator_(std::move(animator)),
      runtime_controller_(std::move(runtime_controller)),
      font_collection_(font_collection),
      image_decoder_(ImageDecoder::Make(settings_,
                                        task_runners,
                                        image_decoder_task_runner,
                                        io_manager,
                                        gpu_disabled_switch)),
      task_runners_(task_runners),
      weak_factory_(this) {
  pointer_data_dispatcher_ = dispatcher_maker(*this);
}

Engine() [2/2]

flutter::Engine::Engine	(	Delegate &	delegate,
		const PointerDataDispatcherMaker &	dispatcher_maker,
		DartVM &	vm,
		fml::RefPtr< const DartSnapshot >	isolate_snapshot,
		const TaskRunners &	task_runners,
		const PlatformData &	platform_data,
		const Settings &	settings,
		std::unique_ptr< Animator >	animator,
		fml::WeakPtr< IOManager >	io_manager,
		const fml::RefPtr< SkiaUnrefQueue > &	unref_queue,
		fml::TaskRunnerAffineWeakPtr< SnapshotDelegate >	snapshot_delegate,
		std::shared_ptr< VolatilePathTracker >	volatile_path_tracker,
		const std::shared_ptr< fml::SyncSwitch > &	gpu_disabled_switch,
		impeller::RuntimeStageBackend	runtime_stage_type = impeller::RuntimeStageBackend::kSkSL
	)

Creates an instance of the engine. This is done by the Shell on the UI task runner.

Parameters

	delegate	The object used by the engine to perform tasks that require access to components that cannot be safely accessed by the engine. This is the shell.
	dispatcher_maker	The callback provided by PlatformView for engine to create the pointer data dispatcher. Similar to other engine resources, this dispatcher_maker and its returned dispatcher is only safe to be called from the UI thread.
	vm	An instance of the running Dart VM.
[in]	isolate_snapshot	The snapshot used to create the root isolate. Even though the isolate is not DartIsolate::Phase::Running phase, it is created when the engine is created. This requires access to the isolate snapshot upfront.
[in]	task_runners	The task runners used by the shell that hosts this engine.
[in]	settings	The settings used to initialize the shell and the engine.
[in]	animator	The animator used to schedule frames.
[in]	snapshot_delegate	The delegate used to fulfill requests to snapshot a specified scene. The engine cannot snapshot a scene on the UI thread directly because the scene (described via a DisplayList) may reference resources on the GPU and there is no GPU context current on the UI thread. The delegate is a component that has access to all the requisite GPU resources.
[in]	io_manager	The IO manager used by this root isolate to schedule tasks that manage resources on the GPU.

Definition at line 66 of file engine.cc.

    : Engine(delegate,
             dispatcher_maker,
             vm.GetConcurrentWorkerTaskRunner(),
             task_runners,
             settings,
             std::move(animator),
             io_manager,
             std::make_shared<FontCollection>(),
             nullptr,
             gpu_disabled_switch) {
  runtime_controller_ = std::make_unique<RuntimeController>(
      *this,                                 // runtime delegate
      &vm,                                   // VM
      std::move(isolate_snapshot),           // isolate snapshot
      settings_.idle_notification_callback,  // idle notification callback
      platform_data,                         // platform data
      settings_.isolate_create_callback,     // isolate create callback
      settings_.isolate_shutdown_callback,   // isolate shutdown callback
      settings_.persistent_isolate_data,     // persistent isolate data
      UIDartState::Context{
          task_runners_,                           // task runners
          std::move(snapshot_delegate),            // snapshot delegate
          std::move(io_manager),                   // io manager
          unref_queue,                             // Skia unref queue
          image_decoder_->GetWeakPtr(),            // image decoder
          image_generator_registry_.GetWeakPtr(),  // image generator registry
          settings_.advisory_script_uri,           // advisory script uri
          settings_.advisory_script_entrypoint,    // advisory script entrypoint
          std::move(volatile_path_tracker),        // volatile path tracker
          vm.GetConcurrentWorkerTaskRunner(),      // concurrent task runner
          settings_.enable_impeller,               // enable impeller
          runtime_stage_type,                      // runtime stage type
      });
}

~Engine()

flutter::Engine::~Engine ( )

overridedefault

Destroys the engine engine. Called by the shell on the UI task runner. The running root isolate is terminated and will no longer access the task runner after this call returns. This allows the embedder to tear down the thread immediately if needed.

Member Function Documentation

AddView()

void flutter::Engine::AddView	(	int64_t	view_id,
		const ViewportMetrics &	view_metrics,
		std::function< void(bool added)>	callback
	)

Notify the Flutter application that a new view is available.

        A view must be added before other methods can refer to it,
        including the implicit view. Adding a view that already exists
        triggers an assertion.

Parameters

[in]	view_id	The ID of the new view.
[in]	viewport_metrics	The initial viewport metrics for the view.
[in]	callback	Callback that will be invoked once the engine attempts to add the view.

Definition at line 300 of file engine.cc.

                                                             {
  runtime_controller_->AddView(view_id, view_metrics, std::move(callback));
}

BeginFrame()

void flutter::Engine::BeginFrame	(	fml::TimePoint	frame_time,
		uint64_t	frame_number
	)

Notifies the engine that it is time to begin working on a new frame previously scheduled via a call to Engine::ScheduleFrame. This call originates in the animator.

The frame time given as the argument indicates the point at which the current frame interval began. It is very slightly (because of scheduling overhead) in the past. If a new layer tree is not produced and given to the raster task runner within one frame interval from this point, the Flutter application will jank.

If a root isolate is running, this method calls the ::_beginFrame method in hooks.dart. If a root isolate is not running, this call does nothing.

This method encapsulates the entire UI thread frame workload. The following (mis)behavior in the functioning of the method will cause the jank in the Flutter application:

• The time taken by this method to create a layer-tree exceeds one frame interval (for example, 16.66 ms on a 60Hz display).
• The time take by this method to generate a new layer-tree causes the current layer-tree pipeline depth to change. To illustrate this point, note that maximum pipeline depth used by layer tree in the engine is 2. If both the UI and GPU task runner tasks finish within one frame interval, the pipeline depth is one. If the UI thread happens to be working on a frame when the raster thread is still not done with the previous frame, the pipeline depth is 2. When the pipeline depth changes from 1 to 2, animations and UI interactions that cause the generation of the new layer tree appropriate for (frame_time + one frame interval) will actually end up at (frame_time + two frame intervals). This is not what code running on the UI thread expected would happen. This causes perceptible jank.

Parameters

[in]	frame_time	The point at which the current frame interval began. May be used by animation interpolators, physics simulations, etc..
[in]	frame_number	The frame number recorded by the animator. Used by the framework to associate frame specific debug information with frame timings and timeline events.

Definition at line 263 of file engine.cc.

                                                                      {
  runtime_controller_->BeginFrame(frame_time, frame_number);
}

DispatchPlatformMessage()

void flutter::Engine::DispatchPlatformMessage

(

std::unique_ptr< PlatformMessage >

message

)

Notifies the engine that the embedder has sent it a message. This call originates in the platform view and has been forwarded to the engine on the UI task runner here.

Parameters

[in]

message

The message sent from the embedder to the Dart application.

Definition at line 316 of file engine.cc.

                                                                           {
  std::string channel = message->channel();
  if (channel == kLifecycleChannel) {
    if (HandleLifecyclePlatformMessage(message.get())) {
      return;
    }
  } else if (channel == kLocalizationChannel) {
    if (HandleLocalizationPlatformMessage(message.get())) {
      return;
    }
  } else if (channel == kSettingsChannel) {
    HandleSettingsPlatformMessage(message.get());
    return;
  } else if (!runtime_controller_->IsRootIsolateRunning() &&
             channel == kNavigationChannel) {
    // If there's no runtime_, we may still need to set the initial route.
    HandleNavigationPlatformMessage(std::move(message));
    return;
  }
 
  if (runtime_controller_->IsRootIsolateRunning() &&
      runtime_controller_->DispatchPlatformMessage(std::move(message))) {
    return;
  }
 
  FML_DLOG(WARNING) << "Dropping platform message on channel: " << channel;
}

DispatchPointerDataPacket()

void flutter::Engine::DispatchPointerDataPacket	(	std::unique_ptr< PointerDataPacket >	packet,
		uint64_t	trace_flow_id
	)

Notifies the engine that the embedder has sent it a pointer data packet. A pointer data packet may contain multiple input events. This call originates in the platform view and the shell has forwarded the same to the engine on the UI task runner here.

Parameters

[in]	packet	The pointer data packet containing multiple input events.
[in]	trace_flow_id	The trace flow identifier associated with the pointer data packet. The engine uses this trace identifier to connect trace flows in the timeline from the input event to the frames generated due to those input events. These flows are tagged as "PointerEvent" in the timeline and allow grouping frames and input events into logical chunks.

Definition at line 433 of file engine.cc.

                            {
  TRACE_EVENT0_WITH_FLOW_IDS("flutter", "Engine::DispatchPointerDataPacket",
                             /*flow_id_count=*/1,
                             /*flow_ids=*/&trace_flow_id);
  TRACE_FLOW_STEP("flutter", "PointerEvent", trace_flow_id);
  pointer_data_dispatcher_->DispatchPacket(std::move(packet), trace_flow_id);
}

DispatchSemanticsAction()

void flutter::Engine::DispatchSemanticsAction	(	int	node_id,
		SemanticsAction	action,
		fml::MallocMapping	args
	)

Notifies the engine that the embedder encountered an accessibility related action on the specified node. This call originates on the platform view and has been forwarded to the engine here on the UI task runner by the shell.

Parameters

[in]	node_id	The identifier of the accessibility node.
[in]	action	The accessibility related action performed on the node of the specified ID.
[in]	args	Optional data that applies to the specified action.

Definition at line 443 of file engine.cc.

                                                            {
  runtime_controller_->DispatchSemanticsAction(node_id, action,
                                               std::move(args));
}

DoDispatchPacket()

void flutter::Engine::DoDispatchPacket ( std::unique_ptr< PointerDataPacket >  packet, uint64_t  trace_flow_id  )

overridevirtual

Actually dispatch the packet using Engine's animator_ and runtime_controller_.

Implements flutter::PointerDataDispatcher::Delegate.

Definition at line 528 of file engine.cc.

                                                      {
  animator_->EnqueueTraceFlowId(trace_flow_id);
  if (runtime_controller_) {
    runtime_controller_->DispatchPointerDataPacket(*packet);
  }
}

GetAssetManager()

std::shared_ptr< AssetManager > flutter::Engine::GetAssetManager ( )

overridevirtual

Implements flutter::RuntimeDelegate.

Definition at line 164 of file engine.cc.

                                                    {
  return asset_manager_;
}

GetFontCollection()

FontCollection & flutter::Engine::GetFontCollection ( )

overridevirtual

Implements flutter::RuntimeDelegate.

Definition at line 524 of file engine.cc.

                                          {
  return *font_collection_;
}

GetImageDecoderWeakPtr()

fml::WeakPtr< ImageDecoder > flutter::Engine::GetImageDecoderWeakPtr

(

)

Definition at line 168 of file engine.cc.

                                                        {
  return image_decoder_->GetWeakPtr();
}

GetImageGeneratorRegistry()

fml::WeakPtr< ImageGeneratorRegistry > flutter::Engine::GetImageGeneratorRegistry

(

)

Get the ImageGeneratorRegistry associated with the current engine.

Returns

The engine's ImageGeneratorRegistry.

Definition at line 172 of file engine.cc.

                                                                     {
  return image_generator_registry_.GetWeakPtr();
}

GetLastEntrypoint()

const std::string & flutter::Engine::GetLastEntrypoint

(

)

const

Get the last Entrypoint that was used in the RunConfiguration when |Engine::Run| was called.

Definition at line 563 of file engine.cc.

                                                 {
  return last_entry_point_;
}

GetLastEntrypointArgs()

const std::vector< std::string > & flutter::Engine::GetLastEntrypointArgs

(

)

const

Get the last Entrypoint Arguments that was used in the RunConfiguration when |Engine::Run| was called.This is only valid in debug mode.

Definition at line 571 of file engine.cc.

                                                                {
  return last_entry_point_args_;
}

GetLastEntrypointLibrary()

const std::string & flutter::Engine::GetLastEntrypointLibrary

(

)

const

Get the last Entrypoint Library that was used in the RunConfiguration when |Engine::Run| was called.

Definition at line 567 of file engine.cc.

                                                        {
  return last_entry_point_library_;
}

GetRuntimeController()

const RuntimeController * flutter::Engine::GetRuntimeController ( ) const

inline

Accessor for the RuntimeController.

Definition at line 965 of file engine.h.

                                                        {
    return runtime_controller_.get();
  }

GetUIIsolateLastError()

tonic::DartErrorHandleType flutter::Engine::GetUIIsolateLastError

(

)

Errors that are unhandled on the Dart message loop are kept for further inspection till the next unhandled error comes along. This accessor returns the last unhandled error encountered by the root isolate.

Returns

The ui isolate last error.

Definition at line 296 of file engine.cc.

                                                       {
  return runtime_controller_->GetLastError();
}

GetUIIsolateMainPort()

Dart_Port flutter::Engine::GetUIIsolateMainPort

(

)

Gets the main port of the root isolate. Since the isolate is created immediately in the constructor of the engine, it is possible to get its main port immediately (even before a call to Run can be made). This is useful in registering the port in a race free manner with a port nameserver.

Returns

The main port of the root isolate.

Definition at line 284 of file engine.cc.

                                       {
  return runtime_controller_->GetMainPort();
}

GetUIIsolateName()

std::string flutter::Engine::GetUIIsolateName

(

)

Gets the debug name of the root isolate. By default, the debug name of the isolate is derived from its advisory script URI, advisory main entrypoint and its main port name. For example, "main.dart$main-1234" where the script URI is "main.dart", the entrypoint is "main" and the port name "1234". Once launched, the isolate may re-christen itself using a name it selects via setIsolateDebugName in platform_dispatcher.dart. This name is purely advisory and only used by instrumentation and reporting purposes.

Returns

The debug name of the root isolate.

Definition at line 288 of file engine.cc.

                                   {
  return runtime_controller_->GetIsolateName();
}

GetUIIsolateReturnCode()

std::optional< uint32_t > flutter::Engine::GetUIIsolateReturnCode

(

)

As described in the discussion for UIIsolateHasLivePorts, the "done-ness" of a Dart application is tricky to ascertain and the return value from the main entrypoint is discarded (because the Dart isolate is still running after the main entrypoint returns). But, the concept of an exit code akin to those returned by native applications is still useful. Short lived Dart applications (usually tests), emulate this by setting a per isolate "return value" and then indicating their "done-ness" (usually via closing all live ports). This accessor returns that "return value" is present.

See also

UIIsolateHasLivePorts

Returns

The return code (if specified) by the isolate.

Definition at line 280 of file engine.cc.

                                                     {
  return runtime_controller_->GetRootIsolateReturnCode();
}

GetVsyncWaiter()

const std::weak_ptr< VsyncWaiter > flutter::Engine::GetVsyncWaiter

(

)

const

Definition at line 612 of file engine.cc.

                                                            {
  return animator_->GetVsyncWaiter();
}

GetWeakPtr()

fml::WeakPtr< Engine > flutter::Engine::GetWeakPtr

(

)

const

Returns

The pointer to this instance of the engine. The engine may only be accessed safely on the UI task runner.

Definition at line 155 of file engine.cc.

                                            {
  return weak_factory_.GetWeakPtr();
}

InitialRoute()

const std::string & flutter::Engine::InitialRoute ( ) const

inline

Getter for the initial route. This can be set with a platform message.

Definition at line 898 of file engine.h.

{ return initial_route_; }

LoadDartDeferredLibrary()

void flutter::Engine::LoadDartDeferredLibrary	(	intptr_t	loading_unit_id,
		std::unique_ptr< const fml::Mapping >	snapshot_data,
		std::unique_ptr< const fml::Mapping >	snapshot_instructions
	)

Loads the Dart shared library into the Dart VM. When the Dart library is loaded successfully, the Dart future returned by the originating loadLibrary() call completes.

The Dart compiler may generate separate shared libraries files called 'loading units' when libraries are imported as deferred. Each of these shared libraries are identified by a unique loading unit id. Callers should open and resolve a SymbolMapping from the shared library. The Mappings should be moved into this method, as ownership will be assumed by the dart root isolate after successful loading and released after shutdown of the root isolate. The loading unit may not be used after isolate shutdown. If loading fails, the mappings will be released.

This method is paired with a RequestDartDeferredLibrary invocation that provides the embedder with the loading unit id of the deferred library to load.

Parameters

[in]	loading_unit_id	The unique id of the deferred library's loading unit, as passed in by RequestDartDeferredLibrary.
[in]	snapshot_data	Dart snapshot data of the loading unit's shared library.
[in]	snapshot_data	Dart snapshot instructions of the loading unit's shared library.

Definition at line 589 of file engine.cc.

                                                           {
  if (runtime_controller_->IsRootIsolateRunning()) {
    runtime_controller_->LoadDartDeferredLibrary(
        loading_unit_id, std::move(snapshot_data),
        std::move(snapshot_instructions));
  } else {
    LoadDartDeferredLibraryError(loading_unit_id, "No running root isolate.",
                                 true);
  }
}

LoadDartDeferredLibraryError()

void flutter::Engine::LoadDartDeferredLibraryError	(	intptr_t	loading_unit_id,
		const std::string &	error_message,
		bool	transient
	)

Indicates to the dart VM that the request to load a deferred library with the specified loading unit id has failed.

The dart future returned by the initiating loadLibrary() call will complete with an error.

Parameters

[in]	loading_unit_id	The unique id of the deferred library's loading unit, as passed in by RequestDartDeferredLibrary.
[in]	error_message	The error message that will appear in the dart Future.
[in]	transient	A transient error is a failure due to temporary conditions such as no network. Transient errors allow the dart VM to re-request the same deferred library and loading_unit_id again. Non-transient errors are permanent and attempts to re-request the library will instantly complete with an error.

Definition at line 603 of file engine.cc.

                                                          {
  if (runtime_controller_->IsRootIsolateRunning()) {
    runtime_controller_->LoadDartDeferredLibraryError(loading_unit_id,
                                                      error_message, transient);
  }
}

NotifyDestroyed()

void flutter::Engine::NotifyDestroyed

(

)

Notifies the engine that the attached flutter view has been destroyed. This enables the engine to notify the Dart VM so it can do some cleanp activities.

Definition at line 275 of file engine.cc.

                             {
  TRACE_EVENT0("flutter", "Engine::NotifyDestroyed");
  runtime_controller_->NotifyDestroyed();
}

NotifyIdle()

void flutter::Engine::NotifyIdle

(

fml::TimeDelta

deadline

)

Notifies the engine that the UI task runner is not expected to undertake a new frame workload till a specified timepoint. The timepoint is measured in microseconds against the system's monotonic clock. It is recommended that the clock be accessed via Dart_TimelineGetMicros from dart_api.h for consistency. In reality, the clocks used by Dart, FML and std::steady_clock are all the same and the timepoints can be converted from on clock type to another.

The Dart VM uses this notification to schedule book-keeping tasks that may include a garbage collection. In this way, it is less likely for the VM to perform such (potentially long running) tasks in the middle of a frame workload.

This notification is advisory. That is, not providing this notification does not mean garbage collection is postponed till this call is made. If this notification is not provided, garbage collection will happen based on the usual heuristics used by the Dart VM.

Currently, this idle notification is delivered to the engine at two points. Once, the deadline is calculated based on how much time in the current frame interval is left on the UI task runner. Since the next frame workload cannot begin till at least the next callback from the vsync waiter, this period may be used to used as a "small" idle notification. On the other hand, if no more frames are scheduled, a large (but arbitrary) idle notification deadline is chosen for a "big" idle notification. Again, this notification does not guarantee collection, just gives the Dart VM more hints about opportune moments to perform collections.

Parameters

[in]

deadline

The deadline is used by the VM to determine if the corresponding sweep can be performed within the deadline.

Definition at line 271 of file engine.cc.

                                             {
  runtime_controller_->NotifyIdle(deadline);
}

OnAllViewsRendered()

void flutter::Engine::OnAllViewsRendered ( )

overridevirtual

Implements flutter::RuntimeDelegate.

Definition at line 469 of file engine.cc.

                                {
  animator_->OnAllViewsRendered();
}

RemoveView()

bool flutter::Engine::RemoveView

(

int64_t

view_id

)

Notify the Flutter application that a view is no longer available.

Removing a view that does not exist triggers an assertion.

The implicit view (kFlutterImplicitViewId) should never be removed. Doing so triggers an assertion.

Parameters

[in]

view_id

The ID of the view.

Returns

Whether the view was removed.

Definition at line 306 of file engine.cc.

                                       {
  return runtime_controller_->RemoveView(view_id);
}

ReportTimings()

void flutter::Engine::ReportTimings

(

std::vector< int64_t >

timings

)

Dart code cannot fully measure the time it takes for a specific frame to be rendered. This is because Dart code only runs on the UI task runner. That is only a small part of the overall frame workload. The raster task runner frame workload is executed on a thread where Dart code cannot run (and hence instrument). Besides, due to the pipelined nature of rendering in Flutter, there may be multiple frame workloads being processed at any given time. However, for non-Timeline based profiling, it is useful for trace collection and processing to happen in Dart. To do this, the raster task runner frame workloads need to be instrumented separately. After a set number of these profiles have been gathered, they need to be reported back to Dart code. The shell reports this extra instrumentation information back to Dart code running on the engine by invoking this method at predefined intervals.

See also

FrameTiming

Parameters

[in]

timings

Collection of FrameTiming::kCount * n timestamps for n frames whose timings have not been reported yet. A collection of integers is reported here for easier conversions to Dart objects. The timestamps are measured against the system monotonic clock measured in microseconds.

Definition at line 267 of file engine.cc.

                                                     {
  runtime_controller_->ReportTimings(std::move(timings));
}

Restart()

bool flutter::Engine::Restart

(

RunConfiguration

configuration

)

Tears down an existing root isolate, reuses the components of that isolate and attempts to launch a new isolate using the given the run configuration. This is only used in the "debug" Flutter runtime mode in the cold-restart scenario.

Attention

This operation must be performed with care as even a non-successful restart will still tear down any existing root isolate. In such cases, the engine and its shell must be discarded.

Parameters

[in]

configuration

The configuration used to launch the new isolate.

Returns

Whether the restart was successful. If not, the engine and its shell must be discarded.

Definition at line 201 of file engine.cc.

                                                   {
  TRACE_EVENT0("flutter", "Engine::Restart");
  if (!configuration.IsValid()) {
    FML_LOG(ERROR) << "Engine run configuration was invalid.";
    return false;
  }
  delegate_.OnPreEngineRestart();
  runtime_controller_ = runtime_controller_->Clone();
  UpdateAssetManager(nullptr);
  return Run(std::move(configuration)) == Engine::RunStatus::Success;
}

Run()

Engine::RunStatus flutter::Engine::Run

(

RunConfiguration

configuration

)

Moves the root isolate to the DartIsolate::Phase::Running phase on a successful call to this method.

The isolate itself is created when the engine is created, but it is not yet in the running phase. This is done to amortize initial time taken to launch the root isolate. The isolate snapshots used to run the isolate can be fetched on another thread while the engine itself is launched on the UI task runner.

Repeated calls to this method after a successful run will be rejected even if the run configuration is valid (with the appropriate error returned).

Parameters

[in]

configuration

The configuration used to run the root isolate. The configuration must be valid.

Returns

The result of the call to run the root isolate.

Definition at line 213 of file engine.cc.

                                                          {
  if (!configuration.IsValid()) {
    FML_LOG(ERROR) << "Engine run configuration was invalid.";
    return RunStatus::Failure;
  }
 
  last_entry_point_ = configuration.GetEntrypoint();
  last_entry_point_library_ = configuration.GetEntrypointLibrary();
#if (FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG)
  // This is only used to support restart.
  last_entry_point_args_ = configuration.GetEntrypointArgs();
#endif
 
  UpdateAssetManager(configuration.GetAssetManager());
 
  if (runtime_controller_->IsRootIsolateRunning()) {
    return RunStatus::FailureAlreadyRunning;
  }
 
  // If the embedding prefetched the default font manager, then set up the
  // font manager later in the engine launch process.  This makes it less
  // likely that the setup will need to wait for the prefetch to complete.
  auto root_isolate_create_callback = [&]() {
    if (settings_.prefetched_default_font_manager) {
      SetupDefaultFontManager();
    }
  };
 
  if (!runtime_controller_->LaunchRootIsolate(
          settings_,                                 //
          root_isolate_create_callback,              //
          configuration.GetEntrypoint(),             //
          configuration.GetEntrypointLibrary(),      //
          configuration.GetEntrypointArgs(),         //
          configuration.TakeIsolateConfiguration())  //
  ) {
    return RunStatus::Failure;
  }
 
  auto service_id = runtime_controller_->GetRootIsolateServiceID();
  if (service_id.has_value()) {
    std::unique_ptr<PlatformMessage> service_id_message =
        std::make_unique<flutter::PlatformMessage>(
            kIsolateChannel, MakeMapping(service_id.value()), nullptr);
    HandlePlatformMessage(std::move(service_id_message));
  }
 
  return Engine::RunStatus::Success;
}

ScheduleFrame() [1/2]

void flutter::Engine::ScheduleFrame ( )

inline

Schedule a frame with the default parameter of regenerating the layer tree.

Definition at line 845 of file engine.h.

{ ScheduleFrame(true); }

ScheduleFrame() [2/2]

void flutter::Engine::ScheduleFrame ( bool  regenerate_layer_trees )

overridevirtual

Implements flutter::RuntimeDelegate.

Definition at line 465 of file engine.cc.

                                                      {
  animator_->RequestFrame(regenerate_layer_trees);
}

ScheduleSecondaryVsyncCallback()

void flutter::Engine::ScheduleSecondaryVsyncCallback ( uintptr_t  id, const fml::closure &  callback  )

overridevirtual

Schedule a secondary callback to be executed right after the main VsyncWaiter::AsyncWaitForVsync callback (which is added by Animator::RequestFrame).

Like the callback in AsyncWaitForVsync, this callback is only scheduled to be called once per |id|, and it will be called in the UI thread. If there is no AsyncWaitForVsync callback (Animator::RequestFrame is not called), this secondary callback will still be executed at vsync.

This callback is used to provide the vsync signal needed by SmoothPointerDataDispatcher, and for Animator input flow events.

Implements flutter::PointerDataDispatcher::Delegate.

Definition at line 536 of file engine.cc.

                                                                        {
  animator_->ScheduleSecondaryVsyncCallback(id, callback);
}

SetAccessibilityFeatures()

void flutter::Engine::SetAccessibilityFeatures

(

int32_t

flags

)

Notifies the engine that the embedder has expressed an opinion about where the flags to set on the accessibility tree. This flag originates in the platform view and is forwarded to the engine here on the UI task runner by the shell.

The engine does not care about the accessibility feature flags as all it does is forward this information from the embedder to the framework. However, curious readers may refer to AccessibilityFeatures in window.dart for currently supported accessibility feature flags.

Parameters

[in]

flags

The features to enable in the accessibility tree.

Definition at line 454 of file engine.cc.

                                                   {
  runtime_controller_->SetAccessibilityFeatures(flags);
}

SetDisplays()

void flutter::Engine::SetDisplays

(

const std::vector< DisplayData > &

displays

)

Updates the display metrics for the currently running Flutter application.

Parameters

[in]

displays

A complete list of displays

Definition at line 616 of file engine.cc.

                                                               {
  runtime_controller_->SetDisplays(displays);
  ScheduleFrame();
}

SetSemanticsEnabled()

void flutter::Engine::SetSemanticsEnabled

(

bool

enabled

)

Notifies the engine that the embedder has expressed an opinion about whether the accessibility tree should be generated or not. This call originates in the platform view and is forwarded to the engine here on the UI task runner by the shell.

Parameters

[in]

enabled

Whether the accessibility tree is enabled or disabled.

Definition at line 450 of file engine.cc.

                                             {
  runtime_controller_->SetSemanticsEnabled(enabled);
}

SetupDefaultFontManager()

void flutter::Engine::SetupDefaultFontManager

(

)

Setup default font manager according to specific platform.

Definition at line 159 of file engine.cc.

                                     {
  TRACE_EVENT0("flutter", "Engine::SetupDefaultFontManager");
  font_collection_->SetupDefaultFontManager(settings_.font_initialization_data);
}

SetViewportMetrics()

void flutter::Engine::SetViewportMetrics	(	int64_t	view_id,
		const ViewportMetrics &	metrics
	)

Updates the viewport metrics for a view. The viewport metrics detail the size of the rendering viewport in texels as well as edge insets if present.

See also

ViewportMetrics

Parameters

[in]	view_id	The ID for the view that metrics describes.
[in]	metrics	The metrics.

Definition at line 310 of file engine.cc.

                                                                {
  runtime_controller_->SetViewportMetrics(view_id, metrics);
  ScheduleFrame();
}

ShutdownPlatformIsolates()

void flutter::Engine::ShutdownPlatformIsolates

(

)

Shuts down all registered platform isolates. Must be called from the platform thread.

Definition at line 621 of file engine.cc.

                                      {
  runtime_controller_->ShutdownPlatformIsolates();
}

Spawn()

std::unique_ptr< Engine > flutter::Engine::Spawn	(	Delegate &	delegate,
		const PointerDataDispatcherMaker &	dispatcher_maker,
		const Settings &	settings,
		std::unique_ptr< Animator >	animator,
		const std::string &	initial_route,
		const fml::WeakPtr< IOManager > &	io_manager,
		fml::TaskRunnerAffineWeakPtr< SnapshotDelegate >	snapshot_delegate,
		const std::shared_ptr< fml::SyncSwitch > &	gpu_disabled_switch
	)		const

Create a Engine that shares as many resources as possible with the calling Engine such that together they occupy less memory and be created faster.

This should only be called on running Engines.

Returns

A new Engine with a running isolate.

See also

Engine::Engine

DartIsolate::SpawnIsolate

Definition at line 115 of file engine.cc.

                                                                   {
  auto result = std::make_unique<Engine>(
      /*delegate=*/delegate,
      /*dispatcher_maker=*/dispatcher_maker,
      /*image_decoder_task_runner=*/
      runtime_controller_->GetDartVM()->GetConcurrentWorkerTaskRunner(),
      /*task_runners=*/task_runners_,
      /*settings=*/settings,
      /*animator=*/std::move(animator),
      /*io_manager=*/io_manager,
      /*font_collection=*/font_collection_,
      /*runtime_controller=*/nullptr,
      /*gpu_disabled_switch=*/gpu_disabled_switch);
  result->runtime_controller_ = runtime_controller_->Spawn(
      /*p_client=*/*result,
      /*advisory_script_uri=*/settings.advisory_script_uri,
      /*advisory_script_entrypoint=*/settings.advisory_script_entrypoint,
      /*idle_notification_callback=*/settings.idle_notification_callback,
      /*isolate_create_callback=*/settings.isolate_create_callback,
      /*isolate_shutdown_callback=*/settings.isolate_shutdown_callback,
      /*persistent_isolate_data=*/settings.persistent_isolate_data,
      /*io_manager=*/io_manager,
      /*image_decoder=*/result->GetImageDecoderWeakPtr(),
      /*image_generator_registry=*/result->GetImageGeneratorRegistry(),
      /*snapshot_delegate=*/std::move(snapshot_delegate));
  result->initial_route_ = initial_route;
  result->asset_manager_ = asset_manager_;
  return result;
}

UIIsolateHasLivePorts()

bool flutter::Engine::UIIsolateHasLivePorts

(

)

It is an unexpected challenge to determine when a Dart application is "done". The application cannot simply terminate the native process (and perhaps return an exit code) because it does not have that power. After all, Flutter applications reside within a host process that may have other responsibilities besides just running Flutter applications. Also, the main entry-points are run on an event loop and returning from "main" (unlike in C/C++ applications) does not mean termination of the process. Besides, the return value of the main entrypoint is discarded.

One technique used by embedders to determine "liveness" is to count the outstanding live ports dedicated to the application. These ports may be live as a result of pending timers, scheduled tasks, pending IO on sockets, channels open with other isolates, etc.. At regular intervals (sometimes as often as after the UI task runner processes any task), embedders may check for the "liveness" of the application and perform teardown of the embedder when no more ports are live.

Returns

Check if the root isolate has any live ports.

Definition at line 292 of file engine.cc.

                                   {
  return runtime_controller_->HasLivePorts();
}

UpdateAssetManager()

bool flutter::Engine::UpdateAssetManager

(

const std::shared_ptr< AssetManager > &

asset_manager

)

Updates the asset manager referenced by the root isolate of a Flutter application. This happens implicitly in the call to Engine::Run and Engine::Restart as the asset manager is referenced from the run configuration provided to those calls. In addition to the Engine::Run and Engine::Restart calls, the tooling may need to update the assets available to the application as the user adds them to their project. For example, these assets may be referenced by code that is newly patched in after a hot-reload. Neither the shell or the isolate in relaunched in such cases. The tooling usually patches in the new assets in a temporary location and updates the asset manager to point to that location.

Parameters

[in]

asset_manager

The new asset manager to use for the running root isolate.

Returns

If the asset manager was successfully replaced. This may fail if the new asset manager is invalid.

Definition at line 176 of file engine.cc.

                                                          {
  if (asset_manager_ && new_asset_manager &&
      *asset_manager_ == *new_asset_manager) {
    return false;
  }
 
  asset_manager_ = new_asset_manager;
 
  if (!asset_manager_) {
    return false;
  }
 
  // Using libTXT as the text engine.
  if (settings_.use_asset_fonts) {
    font_collection_->RegisterFonts(asset_manager_);
  }
 
  if (settings_.use_test_fonts) {
    font_collection_->RegisterTestFonts();
  }
 
  return true;
}

Friends And Related Function Documentation

testing::ShellTest

friend class testing::ShellTest

friend

Definition at line 1033 of file engine.h.

---

The documentation for this class was generated from the following files:

• shell/common/engine.h
• shell/common/engine.cc