isolate_flutter

import 'dart:async';
import 'dart:io';
import 'dart:isolate';

class FileRecorder {
  late String _filePath;
  late SendPort _sendPort;
  late ReceivePort _receivePort;
  late Isolate _isolate;
  final Completer<void> _isolateReady = Completer.sync();

  Future<void> start(String filePath) async {
    _filePath = filePath;
    _receivePort = ReceivePort();
    _receivePort.listen(_handleResponsesFromIsolate);
    _isolate = await Isolate.spawn(_startRemoteIsolate, _receivePort.sendPort);
  }

  Future<void> record(List<int> message) async {
    await _isolateReady.future;
    _sendPort.send(message);
  }

  Future<void> stop() async {
    await _isolateReady.future;
    _sendPort.send(true);
  }

  void _handleResponsesFromIsolate(dynamic message) {
    if (message is SendPort) {
      _sendPort = message;
      _isolateReady.complete();
    } else if (message is bool) {
      if (message == true) {
        _receivePort.close();
        _isolate.kill(priority: Isolate.immediate);
      }
    } else if (message is List<int>) {
      final contents = '${message.join(',')},';
      File file = File(_filePath);
      file.writeAsStringSync(contents, mode: FileMode.append);
    }
  }

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

    receivePort.listen((dynamic message) {
      port.send(message);
    });
  }
}

void main() async {
  final ecg = FileRecorder();
  await ecg.start('hello.txt');

  ecg.record(List.generate(1000000, (i) => i));
  ecg.record(List.generate(1000000, (i) => i + 1000000));
  ecg.record(List.generate(1000000, (i) => i + 2000000));
  ecg.record(List.generate(1000000, (i) => i + 3000000));
  ecg.record(List.generate(1000000, (i) => i + 4000000));
  ecg.record(List.generate(1000000, (i) => i + 5000000));

  ecg.stop();
}