Merge "Add common plugin framework."

1 files changed, 86 insertions, 0 deletions

diff --git a/openstack/common/plugin/pluginmanager.py b/openstack/common/plugin/pluginmanager.py
new file mode 100644
index 0000000..0095135
--- /dev/null
+++ b/openstack/common/plugin/pluginmanager.py
@@ -0,0 +1,86 @@
+# 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.
+
+import imp
+import os
+import pkg_resources
+
+from openstack.common import cfg
+from openstack.common import log as logging
+from openstack.common.notifier import list_notifier
+
+
+CONF = cfg.CONF
+LOG = logging.getLogger(__name__)
+
+
+class PluginManager(object):
+    """Manages plugin entrypoints and loading.
+
+    For a service to implement this plugin interface for callback purposes:
+
+      - Make use of the openstack-common notifier system
+      - Instantiate this manager in each process (passing in
+        project and service name)
+
+    For an API service to extend itself using this plugin interface,
+    it needs to query the plugin_extension_factory provided by
+    the already-instantiated PluginManager.
+    """
+
+    def __init__(self, project_name, service_name):
+        """ Construct Plugin Manager; load and initialize plugins.
+
+        project_name (e.g. 'nova' or 'glance') is used
+        to construct the entry point that identifies plugins.
+
+        The service_name (e.g. 'compute') is passed on to
+        each plugin as a raw string for it to do what it will.
+        """
+        self._project_name = project_name
+        self._service_name = service_name
+        self.plugins = []
+
+        # Make sure we're using the list_notifier.
+        if not hasattr(CONF, "list_notifier_drivers"):
+            CONF.list_notifier_drivers = []
+        old_notifier = CONF.notification_driver
+        CONF.notification_driver = 'openstack.common.notifier.list_notifier'
+        if (old_notifier and
+            old_notifier != 'openstack.common.notifier.list_notifier'):
+            list_notifier.add_driver(old_notifier)
+
+    def load_plugins(self):
+        self.plugins = []
+
+        for entrypoint in pkg_resources.iter_entry_points('%s.plugin' %
+                                                          self._project_name):
+            try:
+                pluginclass = entrypoint.load()
+                plugin = pluginclass(self._service_name)
+                self.plugins.append(plugin)
+            except Exception, exc:
+                LOG.error(_("Failed to load plugin %(plug)s: %(exc)s") %
+                          {'plug': entrypoint, 'exc': exc})
+
+        for plugin in self.plugins:
+            for notifier in plugin.notifiers:
+                list_notifier.add_driver(notifier)
+
+    def plugin_extension_factory(self, ext_mgr):
+        for plugin in self.plugins:
+            descriptors = plugin.api_extension_descriptors
+            for descriptor in descriptors:
+                ext_mgr.load_extension(descriptor)