Unhandled Exception: Binding has not yet been initialized - when running Isolate sample example

[shashkiranr]

Steps to reproduce

Run the Isolate example

import 'dart:convert';
import 'dart:isolate';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

const filename = 'json_01.json';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final jsonData = await Isolate.run(() => _readAndParseJson(filename));
  print('Number of JSON keys: ${jsonData.length}');
  runApp(const MyApp());
}

/// Reads the contents of the file with [filename],
/// decodes the JSON, and returns the result.
Future<Map<String, dynamic>> _readAndParseJson(String filename) async {
  final fileData = await rootBundle.loadString('assets/$filename');
  final jsonData = jsonDecode(fileData) as Map<String, dynamic>;
  return jsonData;
}

json_01.json

{
  "a": "foo"
}

tried to replace await Isolate.run(() => _readAndParseJson(filename)) with await compute(_readAndParseJson, filename) and getting the same error

Expected results

Number of JSON keys: 1

Actual results

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Binding has not yet been initialized.
The "instance" getter on the ServicesBinding binding mixin is only available once that binding has been initialized.
Typically, this is done by calling "WidgetsFlutterBinding.ensureInitialized()" or "runApp()" (the latter calls the former). Typically this call is done in the "void main()" method. The "ensureInitialized" method is idempotent; calling it multiple times is not harmful. After calling that method, the "instance" getter will return the binding.
In a test, one can call "TestWidgetsFlutterBinding.ensureInitialized()" as the first line in the test's "main()" method to initialize the binding.
If ServicesBinding is a custom binding mixin, there must also be a custom binding class, like WidgetsFlutterBinding, but that mixes in the selected binding, and that is the class that must be constructed before using the "instance" getter.
#0      BindingBase.checkInstance.<anonymous closure> (pac<…>

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[huycozy]

Hi @shashkiranr
I think you are hitting a similar issue at #130570 that calls platform channel in isolate, please see:

flutter/packages/flutter/lib/src/services/asset_bundle.dart

Lines 315 to 320 in 859a5ab

	class PlatformAssetBundle extends CachingAssetBundle {
	@override
	Future<ByteData> load(String key) {
	final Uint8List encoded = utf8.encode(Uri(path: Uri.encodeFull(key)).path);
	final Future<ByteData>? future = ServicesBinding.instance.defaultBinaryMessenger.send(
	'flutter/assets',

It's marked as a duplicate of #119207. So I'm going to close the issue in favor of this one. Please follow up on it for updates.

[shashkiranr]

I am not using any Platform Channels. Its a basic example of running Isolates from the main function. So you are telling me I can't run the sample isolate example?

[huycozy]

I am not using any Platform Channels.

The rootBundle does, that's why I quoted the code above. The defaultBinaryMessenger will send a binary message to the platform plugins on the given channel:

flutter/packages/flutter/lib/src/services/binary_messenger.dart

Lines 56 to 60 in 66d1872

	/// Send a binary message to the platform plugins on the given channel.
	///
	/// Returns a [Future] which completes to the received response, undecoded,
	/// in binary form.
	Future<ByteData?>? send(String channel, ByteData? message);

You can compare this with a different process like in the sample code below which does I/O task (write to file), the isolate works as expected in this case but reading assets task does not.

Sample code

import 'dart:convert';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter/foundation.dart';
import 'package:path_provider/path_provider.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  // final jsonData = await Isolate.run(() => _readAndParseJson(filename));
  // print('Number of JSON keys: ${jsonData.length}');
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int usingTime = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text("Running time: $usingTime ms"),
            TextButton(onPressed: _runWithIsolate, child: const Text("Run with isolate")),
            TextButton(
                onPressed: _runWithIsolateInPlatformChannel,
                child: const Text("Run with isolate in platform channel")),
          ],
        ),
      ),
    );
  }

  void _runWithIsolate() async {
    var savePath = await getTemporaryDirectory();
    var duration = await compute((path) => _runTask(path), "${savePath.path}/test.log");
    print('With isolate duration: $duration');
    if (mounted) {
      setState(() {
        usingTime = duration;
      });
    }
  }

  static int _runTask(String savePath) {
    var file = File(savePath);
    if (file.existsSync()) {
      file.deleteSync();
    }
    file = File(savePath);
    var startTime = DateTime.now().millisecondsSinceEpoch;
    for (var i = 0; i < 100; i++) {
      file.writeAsStringSync("a\n", mode: FileMode.append);
    }
    return DateTime.now().millisecondsSinceEpoch - startTime;
  }

  void _runWithIsolateInPlatformChannel() async {
    // final jsonData = await Isolate.run(() => _readAndParseJson(filename));
    // print('Number of JSON keys: ${jsonData.length}');
    final jsonData = await compute(_readAndParseJson, 'json_01.json');
    print('Number of JSON keys: ${jsonData}');
  }

  /// Reads the contents of the file with [filename],
  /// decodes the JSON, and returns the result.
  static Future<int> _readAndParseJson(String filename) async {
    final fileData = await rootBundle.loadString('assets/$filename');
    final jsonData = jsonDecode(fileData) as Map<String, String>;
    return jsonData.length;
  }
}

However, when I check the sample code on https://docs.flutter.dev/perf/isolates which also loads assets in isolate, it seems to have worked before. I will re-open this for further insights. The issue is reproduced in the latest Flutter master channel.

flutter doctor -v (stable and master)

[✓] Flutter (Channel stable, 3.19.4, on macOS 14.1 23B74 darwin-x64, locale en-VN)
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    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (3 available)
    • RMX2001 (mobile) • EUYTFEUSQSRGDA6D • android-arm64  • Android 11 (API 30)
    • macOS (desktop)  • macos            • darwin-x64     • macOS 14.1 23B74 darwin-x64
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[✓] Network resources
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• No issues found!

[!] Flutter (Channel master, 3.21.0-16.0.pre.14, on macOS 14.1 23B74 darwin-x64, locale en-VN)
    • Flutter version 3.21.0-16.0.pre.14 on channel master at /Users/huynq/Documents/GitHub/flutter_master
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    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision f5b65bad0f (2 hours ago), 2024-03-27 18:20:55 -0700
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    • If those were intentional, you can disregard the above warnings; however it is recommended to use "git" directly to perform update checks and upgrades.

[✓] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at /Users/huynq/Library/Android/sdk
    • Platform android-34, build-tools 34.0.0
    • ANDROID_HOME = /Users/huynq/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)
    • All Android licenses accepted.

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    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] VS Code (version 1.87.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.84.0

[✓] Connected device (3 available)
    • RMX2001 (mobile) • EUYTFEUSQSRGDA6D • android-arm64  • Android 11 (API 30)
    • macOS (desktop)  • macos            • darwin-x64     • macOS 14.1 23B74 darwin-x64
    • Chrome (web)     • chrome           • web-javascript • Google Chrome 123.0.6312.86

[✓] Network resources
    • All expected network resources are available.

! Doctor found issues in 1 category.

[jonahwilliams]

The sample code loads the string outside of the isolate and passes it in. There should be no copies with strings, so that should work ok.

Closing as this is not a bug or regression.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.