Flutter异步编程-Isolate

import 'dart:isolate';

  external static Future<Isolate> spawn<T>(
      void entryPoint(T message), T message,
      {bool paused: false,
      bool errorsAreFatal,
      SendPort onExit,
      SendPort onError,
      @Since("2.3") String debugName});

//实现newIsolate与rootIsolate(默认)建立连接
import 'dart:isolate';

//定义一个newIsolate
late Isolate newIsolate;
//定义一个newIsolateSendPort, 该newIsolateSendPort需要让rootIsolate持有，
//这样在rootIsolate中就能利用newIsolateSendPort向newIsolate发送消息
late SendPort newIsolateSendPort;

void main() {
  establishConn(); //建立连接
}

//特别需要注意:establishConn执行环境是rootIsolate
void establishConn() async {
  //第1步: 默认执行环境下是rootIsolate，所以创建的是一个rootIsolateReceivePort
  ReceivePort rootIsolateReceivePort = ReceivePort();
  //第2步: 获取rootIsolateSendPort
  SendPort rootIsolateSendPort = rootIsolateReceivePort.sendPort;
  //第3步: 创建一个newIsolate实例，并把rootIsolateSendPort作为参数传入到newIsolate中，为的是让newIsolate中持有rootIsolateSendPort, 这样在newIsolate中就能向rootIsolate发送消息了
  newIsolate = await Isolate.spawn(createNewIsolateContext, rootIsolateSendPort); //注意createNewIsolateContext这个函数执行环境就会变为newIsolate, rootIsolateSendPort就是createNewIsolateContext回调函数的参数
  //第7步: 通过rootIsolateReceivePort接收到来自newIsolate的消息，所以可以注意到这里是await 因为是异步消息
  //只不过这个接收到的消息是newIsolateSendPort, 最后赋值给全局newIsolateSendPort，这样rootIsolate就持有newIsolate的SendPort
  var messageList = await rootIsolateReceivePort.first;
  //第8步，建立连接成功
  print(messageList[0] as String);
  newIsolateSendPort = messageList[1] as SendPort;
}

//特别需要注意:createNewIsolateContext执行环境是newIsolate
void createNewIsolateContext(SendPort rootIsolateSendPort) async {
  //第4步: 注意callback这个函数执行环境就会变为newIsolate, 所以创建的是一个newIsolateReceivePort
  ReceivePort newIsolateReceivePort = ReceivePort();
  //第5步: 获取newIsolateSendPort, 有人可能疑问这里为啥不是直接让全局newIsolateSendPort赋值，注意这里执行环境不是rootIsolate
  SendPort newIsolateSendPort = newIsolateReceivePort.sendPort;
  //第6步: 特别需要注意这里，这里是利用rootIsolateSendPort向rootIsolate发送消息，只不过发送消息是newIsolate的SendPort, 这样rootIsolate就能拿到newIsolate的SendPort
  rootIsolateSendPort.send(['connect success from new isolate', newIsolateSendPort]);
}

Future<R> compute<Q, R>(isolates.ComputeCallback<Q, R> callback, Q message, { String debugLabel }) async {
  if (!kReleaseMode) {
    debugLabel ??= callback.toString();
  }
  final Flow flow = Flow.begin();
  Timeline.startSync('$debugLabel: start', flow: flow);
  final ReceivePort resultPort = ReceivePort();
  final ReceivePort errorPort = ReceivePort();
  Timeline.finishSync();
  final Isolate isolate = await Isolate.spawn<_IsolateConfiguration<Q, FutureOr<R>>>(
    _spawn,
    _IsolateConfiguration<Q, FutureOr<R>>(
      callback,
      message,
      resultPort.sendPort,
      debugLabel,
      flow.id,
    ),
    errorsAreFatal: true,
    onExit: resultPort.sendPort,
    onError: errorPort.sendPort,
  );
  final Completer<R> result = Completer<R>();
  errorPort.listen((dynamic errorData) {
    assert(errorData is List<dynamic>);
    assert(errorData.length == 2);
    final Exception exception = Exception(errorData[0]);
    final StackTrace stack = StackTrace.fromString(errorData[1] as String);
    if (result.isCompleted) {
      Zone.current.handleUncaughtError(exception, stack);
    } else {
      result.completeError(exception, stack);
    }
  });
  resultPort.listen((dynamic resultData) {
    assert(resultData == null || resultData is R);
    if (!result.isCompleted)
      result.complete(resultData as R);
  });
  await result.future;
  Timeline.startSync('$debugLabel: end', flow: Flow.end(flow.id));
  resultPort.close();
  errorPort.close();
  isolate.kill();
  Timeline.finishSync();
  return result.future;
}

//实现newIsolate与rootIsolate互相通信

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

//定义一个newIsolate
late Isolate newIsolate;
//定义一个newIsolateSendPort, 该newIsolateSendPort需要让rootIsolate持有，
//这样在rootIsolate中就能利用newIsolateSendPort向newIsolate发送消息
late SendPort newIsolateSendPort;

void main() {
  establishConn(); //建立连接
}

//特别需要注意:establishConn执行环境是rootIsolate
void establishConn() async {
  //第1步: 默认执行环境下是rootIsolate，所以创建的是一个rootIsolateReceivePort
  ReceivePort rootIsolateReceivePort = ReceivePort();
  //第2步: 获取rootIsolateSendPort
  SendPort rootIsolateSendPort = rootIsolateReceivePort.sendPort;
  //第3步: 创建一个newIsolate实例，并把rootIsolateSendPort作为参数传入到newIsolate中，为的是让newIsolate中持有rootIsolateSendPort, 这样在newIsolate中就能向rootIsolate发送消息了
  newIsolate = await Isolate.spawn(createNewIsolateContext, rootIsolateSendPort); //注意createNewIsolateContext这个函数执行环境就会变为newIsolate, rootIsolateSendPort就是createNewIsolateContext回调函数的参数
  //第7步: 通过rootIsolateReceivePort接收到来自newIsolate的消息，所以可以注意到这里是await 因为是异步消息
  //只不过这个接收到的消息是newIsolateSendPort, 最后赋值给全局newIsolateSendPort，这样rootIsolate就持有newIsolate的SendPort
  newIsolateSendPort = await rootIsolateReceivePort.first;
  //第8步: 建立连接后，在rootIsolate环境下就能向newIsolate发送消息了
  sendMessageToNewIsolate(newIsolateSendPort);
}

//特别需要注意:sendMessageToNewIsolate执行环境是rootIsolate
void sendMessageToNewIsolate(SendPort newIsolateSendPort) async {
  ReceivePort rootIsolateReceivePort = ReceivePort(); //创建专门应答消息rootIsolateReceivePort
  SendPort rootIsolateSendPort = rootIsolateReceivePort.sendPort;
  newIsolateSendPort.send(['this is from root isolate: hello new isolate!', rootIsolateSendPort]);//注意: 为了能接收到newIsolate回复消息需要带上rootIsolateSendPort
  //第11步: 监听来自newIsolate的消息
  print(await rootIsolateReceivePort.first);
}

//特别需要注意:createNewIsolateContext执行环境是newIsolate
void createNewIsolateContext(SendPort rootIsolateSendPort) async {
  //第4步: 注意callback这个函数执行环境就会变为newIsolate, 所以创建的是一个newIsolateReceivePort
  ReceivePort newIsolateReceivePort = ReceivePort();
  //第5步: 获取newIsolateSendPort, 有人可能疑问这里为啥不是直接让全局newIsolateSendPort赋值，注意这里执行环境不是rootIsolate
  SendPort newIsolateSendPort = newIsolateReceivePort.sendPort;
  //第6步: 特别需要注意这里，这里是利用rootIsolateSendPort向rootIsolate发送消息，只不过发送消息是newIsolate的SendPort, 这样rootIsolate就能拿到newIsolate的SendPort
  rootIsolateSendPort.send(newIsolateSendPort);
  //第9步: newIsolateReceivePort监听接收来自rootIsolate的消息
  receiveMsgFromRootIsolate(newIsolateReceivePort);
}

//特别需要注意:receiveMsgFromRootIsolate执行环境是newIsolate
void receiveMsgFromRootIsolate(ReceivePort newIsolateReceivePort) async {
  var messageList = (await newIsolateReceivePort.first) as List;
  print('${messageList[0] as String}');
  final messageSendPort = messageList[1] as SendPort;
  //第10步: 收到消息后，立即向rootIsolate 发送一个回复消息
  messageSendPort.send('this is reply from new isolate: hello root isolate!');
}