Only use special method to send messages to helper isolate.

tools/dom/src/native_DOMImplementation.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.
 
 part of html;
 
 class _Utils {
   static double dateTimeToDouble(DateTime dateTime) =>
       dateTime.millisecondsSinceEpoch.toDouble();
   static DateTime doubleToDateTime(double dateTime) {
@@ skipping 114 matching lines @@
   String putIfAbsent(String key, String ifAbsent()) => Maps.putIfAbsent(this, key, ifAbsent);
   String remove(String key) native "DOMStringMap_remove_Callback";
   void clear() => Maps.clear(this);
   void forEach(void f(String key, String value)) => Maps.forEach(this, f);
   Collection<String> get keys native "DOMStringMap_getKeys_Callback";
   Collection<String> get values => Maps.getValues(this);
   int get length => Maps.length(this);
   bool get isEmpty => Maps.isEmpty(this);
 }
 
-final Future<SendPort> _HELPER_ISOLATE_PORT =
+final Future<SendPort> __HELPER_ISOLATE_PORT =
     spawnDomFunction(_helperIsolateMain);
 
+// Tricky part.
+// Once _HELPER_ISOLATE_PORT gets resolved, it will still delay in .then

[vsm, 2013/04/02 16:08:31]

Extra _ prefix to match the new name.  BTW, do we really have a convention
around using an extra '_'?  Is this any more private than _TIMER_REGISTRY, etc.,
below?

[Anton Muhin, 2013/04/02 16:17:49]

It's my personal invention and probably I shouldn't use it here.

The reason: sometimes I miss a way to point out that some stuff is not supposed
to be used by other code.  Here I sometimes resort to __.  If you think I
shouldn't. I'll fix it.

On 2013/04/02 16:08:31, vsm wrote:

+// and to delay Timer.run is used. However, Timer.run will try to register
+// another Timer and here we got stuck: event cannot be posted as then
+// callback is not executed because it's delayed with timer.
+// Therefore once future is resolved, it's unsafe to call .then on it
+// in Timer code.
+SendPort __SEND_PORT;
+
+_sendToHelperIsolate(msg, SendPort replyTo) {
+  if (__SEND_PORT != null) {
+    __SEND_PORT.send(msg, replyTo);
+  } else {
+    __HELPER_ISOLATE_PORT.then((port) {
+      __SEND_PORT = port;
+      __SEND_PORT.send(msg, replyTo);
+    });
+  }
+}
+
 final _TIMER_REGISTRY = new Map<SendPort, Timer>();
 
 const _NEW_TIMER = 'NEW_TIMER';
 const _CANCEL_TIMER = 'CANCEL_TIMER';
 const _TIMER_PING = 'TIMER_PING';
 const _PRINT = 'PRINT';
 
 _helperIsolateMain() {
   port.receive((msg, replyTo) {
     final cmd = msg[0];
     if (cmd == _NEW_TIMER) {
       final duration = new Duration(milliseconds: msg[1]);
       bool periodic = msg[2];
       ping() { replyTo.send(_TIMER_PING); };
       _TIMER_REGISTRY[replyTo] = periodic ?
           new Timer.periodic(duration, (_) { ping(); }) :
           new Timer(duration, ping);
     } else if (cmd == _CANCEL_TIMER) {
       _TIMER_REGISTRY.remove(replyTo).cancel();
     } else if (cmd == _PRINT) {
       final message = msg[1];
       // TODO(antonm): we need somehow identify those isolates.
       print('[From isolate] $message');
     }
   });
 }
 
 final _printClosure = window.console.log;
 final _pureIsolatePrintClosure = (s) {
-  _HELPER_ISOLATE_PORT.then((sendPort) {
-    sendPort.send([_PRINT, s]);
-  });
+  _sendToHelperIsolate([_PRINT, s]);
 };
 
 final _forwardingPrintClosure = _Utils.forwardingPrint;