new_contents: # Copyright 2011 OpenStack LLC.
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  from openstack.common import cfg
  from openstack.common import importutils
  from openstack.common import log as logging
  
  
  list_notifier_drivers_opt = cfg.MultiStrOpt('list_notifier_drivers',
          default=['openstack.common.notifier.no_op_notifier'],
          help='List of drivers to send notifications')
  
  CONF = cfg.CONF
  CONF.register_opt(list_notifier_drivers_opt)
  
  LOG = logging.getLogger(__name__)
  
  drivers = None
  
  
  class ImportFailureNotifier(object):
      """Noisily re-raises some exception over-and-over when notify is called."""
  
      def __init__(self, exception):
          self.exception = exception
  
      def notify(self, context, message):
          raise self.exception
  
  
  def _get_drivers():
      """Instantiates and returns drivers based on the flag values."""
      global drivers
      if drivers is None:
          drivers = []
          for notification_driver in CONF.list_notifier_drivers:
              try:
                  drivers.append(importutils.import_module(notification_driver))
              except ImportError as e:
                  drivers.append(ImportFailureNotifier(e))
      return drivers
  
  
  def add_driver(notification_driver):
      """Add a notification driver at runtime."""
      # Make sure the driver list is initialized.
      _get_drivers()
      if isinstance(notification_driver, basestring):
          # Load and add
          try:
              drivers.append(importutils.import_module(notification_driver))
          except ImportError as e:
              drivers.append(ImportFailureNotifier(e))
      else:
          # Driver is already loaded; just add the object.
          drivers.append(notification_driver)
  
  
  def _object_name(obj):
      name = []
      if hasattr(obj, '__module__'):
          name.append(obj.__module__)
      if hasattr(obj, '__name__'):
          name.append(obj.__name__)
      else:
          name.append(obj.__class__.__name__)
      return '.'.join(name)
  
  
  def remove_driver(notification_driver):
      """Remove a notification driver at runtime."""
      # Make sure the driver list is initialized.
      _get_drivers()
      removed = False
      if notification_driver in drivers:
          # We're removing an object.  Easy.
          drivers.remove(notification_driver)
          removed = True
      else:
          # We're removing a driver by name.  Search for it.
          for driver in drivers:
              if _object_name(driver) == notification_driver:
                  drivers.remove(driver)
                  removed = True
  
      if not removed:
          raise ValueError("Cannot remove; %s is not in list" %
                           notification_driver)
  
  
  def notify(context, message):
      """Passes notification to multiple notifiers in a list."""
      for driver in _get_drivers():
          try:
              driver.notify(context, message)
          except Exception as e:
              LOG.exception(_("Problem '%(e)s' attempting to send to "
                              "notification driver %(driver)s."), locals())
  
  
  def _reset_drivers():
      """Used by unit tests to reset the drivers."""
      global drivers
      drivers = None
  
subject: Add common logging and notification.