Very simple version of Isolates.

sdk/lib/async/zone.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 dart.async;
 
 typedef dynamic ZoneCallback();
 typedef dynamic ZoneUnaryCallback(arg);
 typedef dynamic ZoneBinaryCallback(arg1, arg2);
 
@@ skipping 683 matching lines @@
     return new _ZoneDelegate(this).createPeriodicTimer(this, duration, f);
   }
 
   void print(String line) {
     new _ZoneDelegate(this).print(this, line);
   }
 }
 
 void _rootHandleUncaughtError(
     Zone self, ZoneDelegate parent, Zone zone, error, StackTrace stackTrace) {
-  _scheduleAsyncCallback(() {
-    print("Uncaught Error: ${error}");
-    var trace = stackTrace;
-    if (trace == null) trace = getAttachedStackTrace(error);
-    // Clear the attached stack trace (if any).
-    _attachStackTrace(error, null);
-    if (trace != null) {
-      print("Stack Trace: \n$trace\n");
-    }
-    throw error;
+  self.run(() {
+    _scheduleAsyncCallback(() {
+      print("Uncaught Error: ${error}");
+      var trace = stackTrace;
+      if (trace == null) trace = getAttachedStackTrace(error);
+      // Clear the attached stack trace (if any).
+      _attachStackTrace(error, null);
+      if (trace != null) {
+        print("Stack Trace: \n$trace\n");
+      }
+      throw error;
+    });
   });
 }
 
 dynamic _rootRun(Zone self, ZoneDelegate parent, Zone zone, f()) {
   if (Zone._current == zone) return f();
 
   Zone old = Zone._current;
   try {
     Zone._current = zone;
     return f();
@@ skipping 118 matching lines @@
   const _RootZone();
 
   Zone get parent => null;
   ZoneSpecification get _specification => const _RootZoneSpecification();
   Zone get _errorZone => this;
 
   bool inSameErrorZone(Zone otherZone) => otherZone._errorZone == this;
 
   operator [](Symbol key) => null;
 
+  dynamic runUnaryGuarded(f, arg) {
+    try {
+      return runUnary(f, arg);
+    } catch (e, s) {
+      return handleUncaughtError(e, s);
+    }
+  }
+
   // Methods that can be customized by the zone specification.
 
   dynamic handleUncaughtError(error, StackTrace stackTrace) =>
       _rootHandleUncaughtError(this, null, this, error, stackTrace);
 
   Zone fork({ZoneSpecification specification, Map zoneValues}) =>
       _rootFork(this, null, this, specification, zoneValues);
 
   dynamic run(f()) => _rootRun(this, null, this, f);
 
@@ skipping 149 matching lines @@
   ZoneSpecification specification =
     new ZoneSpecification(handleUncaughtError: errorHandler,
                           scheduleMicrotask: asyncHandler);
   Zone zone = Zone.current.fork(specification: specification);
   if (onError != null) {
     return zone.runGuarded(body);
   } else {
     return zone.run(body);
   }
 }