Fix bug 846:

bin/timer_impl.dart

 // Copyright (c) 2011, 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.
 
 class _Timer implements Timer {
 
   /*
    * Set jitter to wake up timer events that would happen in _TIMER_JITTER ms.
    */
   static final int _TIMER_JITTER = 0;
 
   /*
    * Disables the timer.
    */
   static final int _NO_TIMER = -1;
 
   factory _Timer(void callback(Timer timer),
                  int milliSeconds,
                  bool repeating) {
     EventHandler._start();
     if (_timers === null) {
       _timers = new DoubleLinkedQueue<_Timer>();
     }
     Timer timer = new _Timer._internal();
     timer._callback = callback;
     timer._milliSeconds = milliSeconds;
     timer._wakeupTime = (new Date.now()).value + milliSeconds;
     timer._repeating = repeating;
     timer._addTimerToList();
     timer._notifyEventHandler();

[siva, 2011/12/16 01:42:02]

We need to call notifyEventHandler only if addTimerToList added this new timer
object as the first element of the timer list. This would further cut down calls
to notifyEventHandler.

     return timer;
   }
 
   _Timer._internal() {}
 
   void _clear() {
     _callback = null;
     _milliSeconds = 0;
     _wakeupTime = 0;
     _repeating = false;
@@ skipping 27 matching lines @@
 
   /*
    * Adds a timer to the timer list and resets the native timer if it is the
    * earliest timer in the list.  Timers with the same wakeup time are enqueued
    * in order and notified in FIFO order.
    */
   void _addTimerToList() {
     if (_callback !== null) {
 
       DoubleLinkedQueueEntry<_Timer> entry = _timers.firstEntry();
-      if (entry === null) {
-        _createTimerHandler();
-      }
-
       while (entry !== null) {
         if (_wakeupTime < entry.element._wakeupTime) {
           entry.prepend(this);
           return;
         }
         entry = entry.nextEntry();
       }
       _timers.addLast(this);
     }
   }
 
 
   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);
     }
   }
 
 
   /*
    * Creates a receive port and registers the timer handler on that receive
    * port.
    */
   void _createTimerHandler() {
 
     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();
-          timer._callback(timer);
-          // Always process the event with the earliest wakeupTime first.
+          pending_timers.addLast(timer);
           entry = _timers.firstEntry();
-          if (timer._repeating) {
-            timer._advanceWakeupTime();
-            timer._addTimerToList();
-            _notifyEventHandler();
-          }
         } 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);
+          if (timer._repeating) {
+            timer._advanceWakeupTime();
+            timer._addTimerToList();
+          }
+        }
+      } finally {
+        _handling_callbacks = false;
+      }
       _notifyEventHandler();
     }
 
     if(_receivePort === null) {
       _receivePort = new ReceivePort();
       _receivePort.receive((var message, ignored) {
         _handleTimeout();
       });
     }
   }
 
   void _shutdownTimerHandler() {
     _receivePort.close();
     _receivePort = null;
   }
 
 
   /*
    * Timers are ordered by wakeup time.
    */
   static DoubleLinkedQueue<_Timer> _timers;
 
   static ReceivePort _receivePort;
+  static bool _handling_callbacks = false;
 
   var _callback;
   int _milliSeconds;
   int _wakeupTime;
   bool _repeating;
 }