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# Copyright 2012 OpenStack Foundation.
# 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 log as logging
from openstack.common.plugin import plugin
LOG = logging.getLogger(__name__)
class _CallbackNotifier(object):
"""Manages plugin-defined notification callbacks.
For each Plugin, a CallbackNotifier will be added to the
notification driver list. Calls to notify() with appropriate
messages will be hooked and prompt callbacks.
A callback should look like this:
def callback(context, message, user_data)
"""
def __init__(self):
self._callback_dict = {}
def _add_callback(self, event_type, callback, user_data):
callback_list = self._callback_dict.get(event_type, [])
callback_list.append({'function': callback,
'user_data': user_data})
self._callback_dict[event_type] = callback_list
def _remove_callback(self, callback):
for callback_list in self._callback_dict.values():
for entry in callback_list:
if entry['function'] == callback:
callback_list.remove(entry)
def notify(self, context, message):
if message.get('event_type') not in self._callback_dict:
return
for entry in self._callback_dict[message.get('event_type')]:
entry['function'](context, message, entry.get('user_data'))
def callbacks(self):
return self._callback_dict
class CallbackPlugin(plugin.Plugin):
"""Plugin with a simple callback interface.
This class is provided as a convenience for producing a simple
plugin that only watches a couple of events. For example, here's
a subclass which prints a line the first time an instance is created.
class HookInstanceCreation(CallbackPlugin):
def __init__(self, _service_name):
super(HookInstanceCreation, self).__init__()
self._add_callback(self.magic, 'compute.instance.create.start')
def magic(self):
print "An instance was created!"
self._remove_callback(self, self.magic)
"""
def __init__(self, service_name):
super(CallbackPlugin, self).__init__(service_name)
self._callback_notifier = _CallbackNotifier()
self._add_notifier(self._callback_notifier)
def _add_callback(self, callback, event_type, user_data=None):
"""Add callback for a given event notification.
Subclasses can call this as an alternative to implementing
a fullblown notify notifier.
"""
self._callback_notifier._add_callback(event_type, callback, user_data)
def _remove_callback(self, callback):
"""Remove all notification callbacks to specified function."""
self._callback_notifier._remove_callback(callback)
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