Fix bug 846:

bin/timer_impl.dart

Index: bin/timer_impl.dart
===================================================================
--- bin/timer_impl.dart	(revision 2499)
+++ bin/timer_impl.dart	(working copy)
@@ -75,10 +75,6 @@
     if (_callback !== null) {
 
       DoubleLinkedQueueEntry<_Timer> entry = _timers.firstEntry();
-      if (entry === null) {
-        _createTimerHandler();
-      }
-
       while (entry !== null) {
         if (_wakeupTime < entry.element._wakeupTime) {
           entry.prepend(this);
@@ -92,12 +88,26 @@
 
 
   void _notifyEventHandler() {
+    if (_handling_callbacks) {
+      // While we are already handling callbacks we will not notify the event
+      // handler. _handleTimeout will call _notifyEventHandler once all pending
+      // timers are processed.
+      return;
+    }
+
     if (_timers.firstEntry() === null) {
+      // No pending timers: Close the receive port and let the event handler
+      // know.
       if (_receivePort !== null) {
         EventHandler._sendData(-1, _receivePort, _NO_TIMER);
         _shutdownTimerHandler();
       }
     } else {
+      if (_receivePort === null) {
+        // Create a receive port and register a message handler for the timer
+        // events.
+        _createTimerHandler();
+      }
       EventHandler._sendData(-1,
                              _receivePort,
                              _timers.firstEntry().element._wakeupTime);
@@ -114,22 +124,34 @@
     void _handleTimeout() {
       int currentTime = (new Date.now()).value + _TIMER_JITTER;
 
+      // Collect all pending timers.
       DoubleLinkedQueueEntry<_Timer> entry = _timers.firstEntry();
+      var pending_timers = new List();
       while (entry !== null) {
         _Timer timer = entry.element;
         if (timer._wakeupTime <= currentTime) {
           entry.remove();
+          pending_timers.addLast(timer);
+          entry = _timers.firstEntry();
+        } else {
+          break;
+        }
+      }
+
+      // Trigger all of the pending timers. New timers added as part of the
+      // callbacks will be enqueued now and notified in the next spin at the
+      // earliest.
+      _handling_callbacks = true;
+      try {
+        for (var timer in pending_timers) {
           timer._callback(timer);
-          // Always process the event with the earliest wakeupTime first.
-          entry = _timers.firstEntry();
           if (timer._repeating) {
             timer._advanceWakeupTime();
             timer._addTimerToList();
-            _notifyEventHandler();
           }
-        } else {
-          break;
         }
+      } finally {
+        _handling_callbacks = false;
       }
       _notifyEventHandler();
     }
@@ -154,6 +176,7 @@
   static DoubleLinkedQueue<_Timer> _timers;
 
   static ReceivePort _receivePort;
+  static bool _handling_callbacks = false;
 
   var _callback;
   int _milliSeconds;