// 1. Define the async operation
Future<String> fetchUserData() async {
  await Future.delayed(const Duration(seconds: 2)); // Simulate network I/O
  return "User Data Loaded";
}

// 2. Consume in the UI
Widget build(BuildContext context) {
  return FutureBuilder<String>(
    future: fetchUserData(),
    builder: (context, snapshot) {
      if (snapshot.connectionState == ConnectionState.waiting) {
        return const CircularProgressIndicator();
      } else if (snapshot.hasError) {
        return Text('Error: ${snapshot.error}');
      } else {
        return Text('Result: ${snapshot.data}');
      }
    },
  );
}

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

// 1. Define the heavy computation callback
// Note: Adhering to the strict single-argument signature requirement.
List<dynamic> decodeHeavyJson(String jsonString) {
  return jsonDecode(jsonString) as List<dynamic>;
}

// 2. Offload to a worker isolate
Future<List<dynamic>> processDataInBackground(String rawJson) async {
  // Isolate.run spawns the isolate, runs the computation, returns the value, and exits.
  final result = await Isolate.run(() => decodeHeavyJson(rawJson));
  return result;
}

import 'dart:isolate';

class WorkerManager {
  late SendPort _workerSendPort;
  final ReceivePort _mainReceivePort = ReceivePort();
  Isolate? _isolate;

  Future<void> initialize() async {
    // 1. Spawn isolate and pass the Main Isolate's SendPort
    _isolate = await Isolate.spawn(_workerEntry, _mainReceivePort.sendPort);

    // 2. Listen for messages from the Worker Isolate
    _mainReceivePort.listen((message) {
      if (message is SendPort) {
        // First message is the Worker's SendPort
        _workerSendPort = message;
        _startCommunication();
      } else {
        // Subsequent messages are data payloads
        print('Main Isolate received: $message');
      }
    });
  }

  void _startCommunication() {
    // Send data to the worker
    _workerSendPort.send("Process this data");
  }

  // 3. Worker Isolate Entry Point
  static void _workerEntry(SendPort mainSendPort) {
    final workerReceivePort = ReceivePort();
    
    // Send the Worker's SendPort back to the Main Isolate
    mainSendPort.send(workerReceivePort.sendPort);

    // Listen for incoming tasks
    workerReceivePort.listen((message) {
      print('Worker Isolate received: $message');
      
      // Perform work and send result back
      final result = "Processed: $message";
      mainSendPort.send(result);
    });
  }

  void dispose() {
    _mainReceivePort.close();
    _isolate?.kill();
  }
}