Dart: Isolate Example [Courtesy: Forian Loitsch]. NOTE: This example is not maintained. Please see https://github.com/dartlang-italia/dart-libraries-samples/tree/master/isolate for a working example.

spawn.dart

void echo(SendPort initialReplyTo) {
  var port = new ReceivePort();
  initialReplyTo(port.sendPort);
  port.listen((msg) {
    var data = msg[0];
    SendPort replyTo = msg[1];
    replyTo.send(data);
    if (data == "bar") port.close();
  });
}

Future sendReceive(SendPort port, msg) {
  ReceivePort response = new ReceivePort();
  port.send([msg, response.sendPort]);
  return response.first;
}

main() {
  var response = new ReceivePort();
  Future<Isolate> remote = Isolate.spawn(echo, response.sendPort);
  remote.then((_) => response.first).then((sendPort) {
    sendReceive(sendPort, "foo").then((msg) {
      print("received: $msg");
      return sendReceive(sendPort, "bar");
    }).then((msg) {
      print("received another: $msg");
    });
  });
}

spawnUri.dart

// == new file echo.dart.
void main(List<String> args, SendPort replyTo) {
  replyTo.send(args[0]);
}

// == new file start.dart
main() {
  var response = new ReceivePort();
  Future<Isolate> remote = Isolate.spawnUri(Uri.parse("echo.dart"), ["foo"], response.sendPort);
  remote.then((_) => response.first)
    .then((msg) { print("received: $msg"); });
}

Courtesy: https://groups.google.com/a/dartlang.org/forum/#!topic/misc/EVUMkZXFXtY

A couple of tweaks to spawn.dart?

Add imports

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

Fix use of initial reply

  initialReplyTo.send(port.sendPort);

...and always, you get points for ending a file in a new line 😄

Hello. I found this gist in google.

Please help he understand why code from this example don't want to be async.
I added
print('main'); after line 20,
sleep(new Duration(seconds: 5)); after line 29,
gist: https://gist.github.com/jamm/ae279f23cbd106e1d0fd
and result is:

main
// here we are waiting 5 seconds
received: foo
received another: bar

what's the case of spawning isolate if it waits for main thread?