1 files changed, 46 insertions, 0 deletions
diff --git a/openstack/common/scheduler/base_handler.py b/openstack/common/scheduler/base_handler.py
new file mode 100644
index 0000000..147d90d
--- /dev/null
+++ b/openstack/common/scheduler/base_handler.py
@@ -0,0 +1,46 @@
+# Copyright (c) 2011-2013 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.
+"""
+A common base for handling extension classes.
+
+Used by BaseFilterHandler and BaseWeightHandler
+"""
+
+import inspect
+
+from stevedore import extension
+
+
+class BaseHandler(object):
+    """ Base class to handle loading filter and weight classes.
+    """
+    def __init__(self, modifier_class_type, modifier_namespace):
+        self.namespace = modifier_namespace
+        self.modifier_class_type = modifier_class_type
+        self.extension_manager = extension.ExtensionManager(modifier_namespace)
+
+    def _is_correct_class(self, cls):
+        """Return whether an object is a class of the correct type and
+        is not prefixed with an underscore.
+        """
+        return (inspect.isclass(cls) and
+                not cls.__name__.startswith('_') and
+                issubclass(cls, self.modifier_class_type))
+
+    def get_all_classes(self):
+        # We use a set, as some classes may have an entrypoint of their own,
+        # and also be returned by a function such as 'all_filters' for example
+        return [ext.plugin for ext in self.extension_manager if
+                self._is_correct_class(ext.plugin)]