From 856503b064e79bc0daf1d27bf2ce1fa4ecd62160 Mon Sep 17 00:00:00 2001
From: Andrew Bogott <abogott@wikimedia.org>
Date: Wed, 13 Jun 2012 11:51:32 -0500
Subject: Add common plugin framework.

For blueprint novaplugins.

It turns out that most of the plugin framework applies equally well
to other projects, so it's going into Nova via common so that
other projects can pull it in with a minimum of fuss.

Change-Id: Ia4455a8ca0b8c1c3e4b0b9647e8cacaf0a47c914
---
 openstack/common/plugin/callbackplugin.py | 93 +++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 openstack/common/plugin/callbackplugin.py

(limited to 'openstack/common/plugin/callbackplugin.py')

diff --git a/openstack/common/plugin/callbackplugin.py b/openstack/common/plugin/callbackplugin.py
new file mode 100644
index 0000000..bb56a40
--- /dev/null
+++ b/openstack/common/plugin/callbackplugin.py
@@ -0,0 +1,93 @@
+# Copyright 2012 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.plugin import plugin
+from openstack.common import log as logging
+
+
+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)
-- 
cgit