When do hal properties get updated

I'm calling GetProperty on a org.freedesktop.Hal.Device from my handler during a PropertyNotified signal. I'm only calling GetProperty on properties that have been added or changed.

When I call GetProperty during property adds, I'm getting a org.freedesktop.Hal.NoSuchProperty exception. I'm also worried that during changes, I'm getting the old values.

When should I be calling GetProperty? What race conditions are involved?

From stackoverflow

• How about DeviceExists method (like here):

      if device.PropertyExists('info.product'):
          return device.GetProperty('info.product')
      return "unknown"
  

  And PropertyModified signal, (ex from real world):

   #
   # _CBHalDeviceConnected
   #
   # INTERNAL
   #
   # Callback triggered when a device is connected through Hal.
   #
  
   def _CBHalDeviceConnected(self, obj_path): 
  ...
   self.device.connect_to_signal("PropertyModified", 
     self._CBHalDeviceAuthStateChanged) 
  ...
  
  #
  # _CBHalDeviceAuthStateChanged
  #
  # INTERNAL
  #
  # Callback triggered when a Hal device property is changed, 
  # for checking authorization state changes
  #
  
  def _CBHalDeviceAuthStateChanged(self,num_changes,properties):
   for property in properties:
   property_name, added, removed = property
   if property_name == "pda.pocketpc.password":
   self.logger.info("_CBHalDeviceAuthStateChanged: 
       device authorization state changed: reauthorizing")
   self._ProcessAuth()
  

  HAL 0.5.10 Specification
  D-Bus Specification
  D-Bus Tutorial