medium_01_isolates_timer.dart

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

main(List<String> args) async {
  stdout.writeln("isolate running the 'main' method is called: " +
      Isolate.current.debugName);

  // creates a port to receive messages on MainIsolate
  final mainControlPort = ReceivePort();

  // Spawns reates a new isolate
  // Once it's start, it will run the "timerTick" function and
  // the param will be the "mainControlPort.sendPort".
  // This away it can send messages back to the "parent" main Isolate when needed
  Isolate timerIsolate;
  timerIsolate = await Isolate.spawn(
    timerTick,
    mainControlPort.sendPort,
    debugName: "TimerIsolate",
  );

  // mainControlPort is a normal stream, transform it in a broadcast one
  // this way we can listen it in more than one place: (1) and (2)
  final streamOfMesssage = mainControlPort.asBroadcastStream();

  // (1)
  // Send a message to TimerIsolate start itself
  stdout.writeln(Isolate.current.debugName + " asking TimerIsolate to start");
  SendPort timer = await streamOfMesssage.first;
  timer.send("start");

  // (2)
  // Keep listening messages from TimerIsolate until we receive 10 messages
  // then kill both "MainIsolate" and "TimerIsolate"
  var counter = 0;
  streamOfMesssage.listen(
    (message) {
      counter++;
      if (counter == 10) {
        stdout.writeln("finishing timer...");
        timerIsolate.kill();
        stdout.writeln("finishing main...");
        Isolate.current.kill();
      } else {
        stdout.writeln(message);
      }
    },
  );
}

void timerTick(SendPort mainPort) async {
  final timerControlPort = ReceivePort();
  stdout.writeln(Isolate.current.debugName + " started");

  mainPort.send(timerControlPort.sendPort);

  await timerControlPort.firstWhere((message) => message == "start");

  stdout.writeln(Isolate.current.debugName + " will start sending messages...");

  Timer.periodic(Duration(seconds: 1), (timer) {
    mainPort.send(DateTime.now().toIso8601String());
  });
}