Very simple version of Isolates.

tests/isolate/spawn_function_custom_class_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Create a user-defined class in a new isolate.
 //
 // Regression test for vm bug 2235: We were forgetting to finalize
 // classes in new isolates started using the v2 api.
 
 library spawn_tests;
 import 'dart:isolate';
 import '../../pkg/unittest/lib/unittest.dart';
 
 class MyClass {
   var myVar = 'there';
   myFunc(msg) {
     return '$msg $myVar';
   }
 }
 
-child() {
-  port.receive((msg, reply) {
-    reply.send('re: ${new MyClass().myFunc(msg)}');
-  });
+child(args) {
+  var reply = args[1];
+  var msg = args[0];
+  reply.send('re: ${new MyClass().myFunc(msg)}');
 }
 
 main() {
   test('message - reply chain', () {
     ReceivePort port = new ReceivePort();
-    port.receive((msg, _) {
+    Isolate.spawn(child, ['hi', port.sendPort]);
+    port.listen((msg) {
       port.close();
       expect(msg, equals('re: hi there'));
     });
-
-    SendPort s = spawnFunction(child);
-    s.send('hi', port.toSendPort());
   });
 }