Dart多线程开发与实现指南

一、基础 Isolate 使用

场景：计算密集型任务

import 'dart:isolate';

void main() async {
  // 创建接收端口
  final receivePort = ReceivePort();

  // 启动新 Isolate
  await Isolate.spawn(
    fibonacciIsolate,
    {'sendPort': receivePort.sendPort, 'n': 40},
  );

  // 监听结果
  receivePort.listen((message) {
    print('斐波那契结果: $message');
    receivePort.close();
  });
}

void fibonacciIsolate(Map<String, dynamic> data) {
  final sendPort = data['sendPort'] as SendPort;
  final n = data['n'] as int;
  sendPort.send(fibonacci(n));
}

int fibonacci(int n) {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

---

二、长时间后台任务

场景：定时上报进度

void main() async {
  final receivePort = ReceivePort();
  await Isolate.spawn(backgroundTask, receivePort.sendPort);

  receivePort.listen((progress) {
    print('当前进度: $progress%');
    if (progress >= 100) receivePort.close();
  });
}

void backgroundTask(SendPort sendPort) {
  for (int i = 0; i <= 100; i += 10) {
    sendPort.send(i);
    // 模拟耗时操作
    Isolate.sleep(Duration(seconds: 1));
  }
}

---

三、多 Isolate 协作

场景：并行处理多个任务

void main() async {
  final results = await Future.wait([
    compute(fibonacci, 40),
    compute(factorial, 20),
  ]);
  print('结果: $results');
}

int factorial(int n) => n == 0 ? 1 : n * factorial(n - 1);

---

四、双向通信

场景：主 Isolate 与子 Isolate 对话

void main() async {
  final mainReceivePort = ReceivePort();
  final isolate = await Isolate.spawn(
    echoIsolate,
    mainReceivePort.sendPort,
  );

  mainReceivePort.listen((message) {
    print('收到: $message');
    if (message == 'Hello') {
      (message as SendPort).send('你好，子 Isolate!');
    }
  });

  // 发送初始消息
  mainReceivePort.sendPort.send('Hello');
}

void echoIsolate(SendPort mainSendPort) {
  final isolateReceivePort = ReceivePort();
  mainSendPort.send(isolateReceivePort.sendPort);

  isolateReceivePort.listen((message) {
    print('子收到: $message');
    mainSendPort.send('收到: $message');
  });
}

---

五、使用 compute 简化操作

场景：快速并行计算

import 'dart:async';
import 'package:flutter/foundation.dart';

void main() async {
  final result = await compute(fibonacci, 40);
  print('计算结果: $result');
}

---

关键概念总结

1. 内存隔离：Isolate 间不共享内存，通过 SendPort 传递可序列化数据。
2. 错误处理：在 Isolate 内使用 try-catch 捕获异常，通过端口发送错误信息。
3. 性能考量：适合 CPU 密集型任务，避免用于高频小消息通信。
4. Flutter 集成：使用 compute 在 Flutter 中简化后台任务，防止 UI 卡顿。

错误处理示例

void main() async {
  final receivePort = ReceivePort();
  await Isolate.spawn(
    errorTask,
    receivePort.sendPort,
    onError: receivePort.sendPort, // 错误发送到主端口
    onExit: receivePort.sendPort,
  );

  receivePort.listen((message) {
    if (message is List && message[0] is String) {
      print('错误: ${message[1]}');
    } else {
      print('结果: $message');
    }
    receivePort.close();
  });
}

void errorTask(SendPort sendPort) {
  try {
    // 可能出错的操作
    final result = someDangerousOperation();
    sendPort.send(result);
  } catch (e) {
    sendPort.send(['error', e.toString()]);
  }
}