[beta] [wasm] is isolates supported or I'm doing something wrong? (Unsupported operation: ReceivePort)

[d-polikhranidi]

Steps to reproduce

1. ensure that you're on beta channel
2. copy example code to main.dart
3. build with flutter build web --wasm
4. serve it with dhttpd '--headers=Cross-Origin-Embedder-Policy=credentialless;Cross-Origin-Opener-Policy=same-origin' from build/web folder
5. click on FAB
6. look at errors in developer console((

Same behavior with Isolate.run and compute()

Is Isolates not supported in WASM or I'm doing Isolates in wrong way?

Expected results

Code will run in separate thread

Actual results

Throwing an Exception and not executes

Code sample

Code sample

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

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: const Center(
        child: FlutterLogo(size: 200),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () async {
          final worker = Worker();
          await worker.spawn();
          await worker.parseJson('{"key":"value"}');
        },
        child: const Icon(Icons.run_circle),
      ),
    );
  }
}

class Worker {
  late SendPort _sendPort;
  final Completer<void> _isolateReady = Completer.sync();

  Future<void> spawn() async {
    final receivePort = ReceivePort();
    receivePort.listen(_handleResponsesFromIsolate);
    await Isolate.spawn(_startRemoteIsolate, receivePort.sendPort);
  }

  void _handleResponsesFromIsolate(dynamic message) {
    if (message is SendPort) {
      _sendPort = message;
      _isolateReady.complete();
    } else if (message is Map<String, dynamic>) {
      print(message);
    }
  }

  static void _startRemoteIsolate(SendPort port) {
    final receivePort = ReceivePort();
    port.send(receivePort.sendPort);

    receivePort.listen((dynamic message) async {
      if (message is String) {
        final transformed = jsonDecode(message);
        port.send(transformed);
      }
    });
  }

  Future<void> parseJson(String message) async {
    await _isolateReady.future;
    _sendPort.send(message);
  }
}

Flutter Doctor output

Doctor output

[✓] Flutter (Channel beta, 3.21.0-1.0.pre.2, on macOS 14.3.1 23D60 darwin-arm64, locale ru-BY)
    • Flutter version 3.21.0-1.0.pre.2 on channel beta at /Users/admin/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision c398442c35 (26 hours ago), 2024-03-12 22:26:24 -0700
    • Engine revision 0d4f78c952
    • Dart version 3.4.0 (build 3.4.0-190.1.beta)
    • DevTools version 2.33.1

[✓] Android toolchain - develop for Android devices (Android SDK version 33.0.2)
    • Android SDK at /Users/admin/Library/Android/sdk
    • Platform android-33, build-tools 33.0.2
    • Java binary at: /Users/admin/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.

[✓] Xcode - develop for iOS and macOS (Xcode 15.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 15E204a
    • CocoaPods version 1.14.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2023.2)
    • Android Studio at /Users/admin/Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.9+0-17.0.9b1087.7-11185874)

[✓] Connected device (5 available)
    • iPhone (XXXX) (mobile)         • XXX-XXXXX            • ios            • iOS 17.3.1 21D61
    • iPhone 15 Pro Max (mobile)      • XXXX-XX-XX-XX-XXXXXX • ios            • com.apple.CoreSimulator.SimRuntime.iOS-17-4 (simulator)
    • macOS (desktop)                 • macos                                • darwin-arm64   • macOS 14.3.1 23D60 darwin-arm64
    • Mac Designed for iPad (desktop) • mac-designed-for-ipad                • darwin         • macOS 14.3.1 23D60 darwin-arm64
    • Chrome (web)                    • chrome                               • web-javascript • Google Chrome 122.0.6261.129

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

• No issues found!

[mraleph]

Isolates are, currently, not supported on the web and that includes dart2wasm.

[d-polikhranidi]

Isolates are, currently, not supported on the web and that includes dart2wasm.

Thought they would finally be fully supported in WASM. But it's good to hear that they are not supported currently, so is there any chance that there will be support in the future?

[mraleph]

so is there any chance that there will be support in the future?

We would like to support them, but a lot of this depends on whether or not Wasm provides necessary primitives for us to build upon. Specifically I mean proposals like these: https://github.com/WebAssembly/shared-everything-threads/blob/main/proposals/shared-everything-threads/Overview.md

Today we could wire some limited form of isolates but with restrictions on what you can send between them - and all the messages will have to be copied.

[darshankawar]

Based on above comment, I'll close this as not an issue.

[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.