Very simple version of Isolates.

tests/standalone/io/testing_server.dart

 // Copyright (c) 2013, 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.
 
 part of ServerTest;
 
 abstract class TestingServer {
 
   static const HOST = "127.0.0.1";
   static const INIT = 0;
   static const SHUTDOWN = -1;
 
   void onConnection(Socket connection);  // Abstract.
 
   void errorHandlerServer(e) {
     String msg = "Server socket error $e";
     var trace = getAttachedStackTrace(e);
     if (trace != null) msg += "\nStackTrace: $trace";
     Expect.fail(msg);
   }
 
-  void dispatch(message, SendPort replyTo) {
-    if (message == INIT) {
-      ServerSocket.bind(HOST, 0).then((server) {
-        _server = server;
-        _server.listen(
-            onConnection,
-            onError: errorHandlerServer);
-        replyTo.send(_server.port, null);
-      });
-    } else if (message == SHUTDOWN) {
-      _server.close();
-      port.close();
-    }
+  SendPort get closeSendPort => _closePort.sendPort;
+
+  Future<int> init() {
+    _closePort = new ReceivePort();
+    _closePort.first.then((_) { close(); });
+    return ServerSocket.bind(HOST, 0).then((server) {
+      _server = server;
+      _server.listen(
+          onConnection,
+          onError: errorHandlerServer);
+      return _server.port;
+    });
+  }
+
+  void close() {
+    _server.close();
   }
 
   ServerSocket _server;
+  ReceivePort _closePort;
 }
-
-abstract class TestingServerTest {
-
-  TestingServerTest.start(SendPort port)
-      : _receivePort = new ReceivePort(),
-        _sendPort = port {
-    initialize();
-  }
-
-  void run();  // Abstract.
-
-  void initialize() {
-    _receivePort.receive((var message, SendPort replyTo) {
-      _port = message;
-      run();
-    });
-    _sendPort.send(TestingServer.INIT, _receivePort.toSendPort());
-  }
-
-  void shutdown() {
-    _sendPort.send(TestingServer.SHUTDOWN, _receivePort.toSendPort());
-    _receivePort.close();
-  }
-
-  int _port;
-  ReceivePort _receivePort;
-  SendPort _sendPort;
-}