dart_ui_isolate

This plugin let you run dart:ui in an isolate.

See this issue: flutter/flutter#10647

FlutterEngineGroup Support

Unlike flutter_isolate, dart_ui_isolate supports FlutterEngineGroup.

FlutterEngineGroup makes spawning isolates instant. It also reduces 99% of RAM for spawned isolates.

Note: FlutterEngineGroup is supported on both iOS & Android, but not macOS.

No Platform Plugin Support

Unlike flutter_isolate, dart_ui_isolate does not support calling platform plugins in the spawned isolate.

Why? As of Flutter 3.7, you can call platform plugins from a normal Isolate, i.e. should just use a normal Isolate. In the rare case you need to use both dart:ui & platform plugins from the same isolate, you should preferably use a normal Isolate + dart:ui isolate and pass data between them, or you can use flutter_isolate.

There are a couple more advantages:

1. Removing support for platform plugins makes dart_ui_isolate simpler.
2. Removing support for platform plugins allows FlutterEngineGroup See: rmawatson/flutter_isolate#151

DartUiIsolate API

	Android	iOS	Description
DartUiIsolate.spawn()	✅	✅	spawns a new DartUiIsolate
isolate.pause()	✅	✅	pauses the isolate
isolate.resume()	✅	✅	resumes the isolate
isolate.kill()	✅	✅	kills the an isolate
flutterCompute()	✅	✅	runs code in compute callback

Usage

To spawn a DartUiIsolate, call the spawn() method, or the flutterCompute() method.

Killing

DartUiIsolate requires explict termination with kill().

Why? DartUiIsolate is backed by a platform specific 'view', so the event loop does not automatically terminate when there is no more work left.

MacOS

Due to limitations on Flutter macOS, you must put this code in your /lib/main.dart file.

/lib/main.dart

@pragma('vm:entry-point')
void _flutterIsolateEntryPoint() => DartUiIsolate.macosIsolateInitialize();

Compute Callback

To use an isolate for a single task (like the Flutter compute method), use flutterCompute:

@pragma('vm:entry-point')
Future<int> expensiveWork(int arg) async {
  int result;
  // lots of calculations
  return result;
}

Future<int> doExpensiveWorkInBackground() async {
  return await flutterCompute(expensiveWork, arg);
}

Isolate Entry Point

The isolate entrypoint must be a top-level function, or a class static method.

The isolate entrypoint must decorated with @pragma('vm:entry-point'). Otherwise the app will crash in release mode.

Top-Level Entry Point:

@pragma('vm:entry-point')
void topLevelFunction(Map<String, dynamic> args) {
  // performs work in an isolate
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    DartUiIsolate.spawn(topLevelFunction, {});
    super.initState();
  }

  Widget build(BuildContext context) {
    return Container();
  }
}

Class Static Entry Point:

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  
  @pragma('vm:entry-point')
  static void topLevelFunction(Map<String, dynamic> args) {
    // performs work in an isolate
  }

  @override
  void initState() {
    DartUiIsolate.spawn(_MyAppState.staticMethod, {});
    super.initState();
  }

  Widget build(BuildContext context) {
    return Container();
  }
}

A class-level method will not work and will throw an Exception:

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  
  void classMethod(Map<String, dynamic> args) {
    // don't do this!
  }

  @override
  void initState() {
    // this will throw NoSuchMethodError: The method 'toRawHandle' was called on null.
    DartUiIsolate.spawn(classMethod, {}); 
    super.initState();
  }
  Widget build(BuildContext context) {
    return Container();
  }
}