Very simple version of Isolates.

sdk/lib/io/timer_impl.dart

Index: sdk/lib/io/timer_impl.dart
diff --git a/sdk/lib/io/timer_impl.dart b/sdk/lib/io/timer_impl.dart
index 4939a629bd0b6a1f67c0c5371dc7166489063e9e..d781ed4c0ce6da1e77fb88a24b8454550c7990dd 100644
--- a/sdk/lib/io/timer_impl.dart
+++ b/sdk/lib/io/timer_impl.dart
@@ -11,7 +11,8 @@ class _Timer extends LinkedListEntry<_Timer> implements Timer {
   // Timers are ordered by wakeup time.
   static LinkedList<_Timer> _timers = new LinkedList<_Timer>();
 
-  static ReceivePort _receivePort;
+  static RawReceivePort _receivePort;
+  static StreamSubscription _subscription;

[Ivan Posva, 2013/10/24 06:48:38]

Where is this _subscription used?

[floitsch, 2013/10/24 16:15:58]

spurious code from the ReceivePort -> RawReceivePort transition.
removed.

   static bool _handling_callbacks = false;
 
   Function _callback;
@@ -163,10 +164,7 @@ class _Timer extends LinkedListEntry<_Timer> implements Timer {
     }
 
     if(_receivePort == null) {
-      _receivePort = new ReceivePort();
-      _receivePort.receive((var message, ignored) {
-        _handleTimeout();
-      });
+      _receivePort = new RawReceivePort((message) { _handleTimeout(); });
     }
   }