Add common base weigher/weigher handler for filter scheduler

Filter scheduler is being used for more than one core projects (Nova
and Cinder as of writing), the implementation shared a lot of common
code. This patch is to move base weigher (weighing function), weigher
handler for filter scheduler into oslo to reduce possible porting.

implement bp: common-weights

Change-Id: I2d1b37438663b53e035cc262875a283e5e2ee970

2 files changed, 136 insertions, 0 deletions

diff --git a/openstack/common/scheduler/weight.py b/openstack/common/scheduler/weight.py
new file mode 100644
index 0000000..c5df9da
--- /dev/null
+++ b/openstack/common/scheduler/weight.py
@@ -0,0 +1,91 @@
+# Copyright (c) 2011-2012 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.
+
+"""
+Pluggable Weighing support
+"""
+
+import inspect
+
+from stevedore import extension
+
+
+class WeighedObject(object):
+    """Object with weight information."""
+    def __init__(self, obj, weight):
+        self.obj = obj
+        self.weight = weight
+
+    def __repr__(self):
+        return "<WeighedObject '%s': %s>" % (self.obj, self.weight)
+
+
+class BaseWeigher(object):
+    """Base class for pluggable weighers."""
+    def _weight_multiplier(self):
+        """How weighted this weigher should be.  Normally this would
+        be overriden in a subclass based on a config value.
+        """
+        return 1.0
+
+    def _weigh_object(self, obj, weight_properties):
+        """Override in a subclass to specify a weight for a specific
+        object.
+        """
+        return 0.0
+
+    def weigh_objects(self, weighed_obj_list, weight_properties):
+        """Weigh multiple objects.  Override in a subclass if you need
+        need access to all objects in order to manipulate weights.
+        """
+        constant = self._weight_multiplier()
+        for obj in weighed_obj_list:
+            obj.weight += (constant *
+                           self._weigh_object(obj.obj, weight_properties))
+
+
+class BaseWeightHandler(object):
+    object_class = WeighedObject
+
+    def __init__(self, weighed_object_type, weight_namespace):
+        self.namespace = weight_namespace
+        self.weighed_object_type = weighed_object_type
+        self.weight_manager = extension.ExtensionManager(weight_namespace)
+
+    def _is_correct_class(self, obj):
+        """Return whether an object is a class of the correct type and
+        is not prefixed with an underscore.
+        """
+        return (inspect.isclass(obj) and
+                not obj.__name__.startswith('_') and
+                issubclass(obj, self.weighed_object_type))
+
+    def get_all_classes(self):
+        return [x.plugin for x in self.weight_manager
+                if self._is_correct_class(x.plugin)]
+
+    def get_weighed_objects(self, weigher_classes, obj_list,
+                            weighing_properties):
+        """Return a sorted (highest score first) list of WeighedObjects."""
+
+        if not obj_list:
+            return []
+
+        weighed_objs = [self.object_class(obj, 0.0) for obj in obj_list]
+        for weigher_cls in weigher_classes:
+            weigher = weigher_cls()
+            weigher.weigh_objects(weighed_objs, weighing_properties)
+
+        return sorted(weighed_objs, key=lambda x: x.weight, reverse=True)
diff --git a/openstack/common/scheduler/weights/__init__.py b/openstack/common/scheduler/weights/__init__.py
new file mode 100644
index 0000000..476ff8c
--- /dev/null
+++ b/openstack/common/scheduler/weights/__init__.py
@@ -0,0 +1,45 @@
+# Copyright (c) 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.
+
+"""
+Scheduler host weights
+"""
+
+
+from openstack.common.scheduler import weight
+
+
+class WeighedHost(weight.WeighedObject):
+    def to_dict(self):
+        return {
+            'weight': self.weight,
+            'host': self.obj.host,
+        }
+
+    def __repr__(self):
+        return ("WeighedHost [host: %s, weight: %s]" %
+                (self.obj.host, self.weight))
+
+
+class BaseHostWeigher(weight.BaseWeigher):
+    """Base class for host weights."""
+    pass
+
+
+class HostWeightHandler(weight.BaseWeightHandler):
+    object_class = WeighedHost
+
+    def __init__(self, namespace):
+        super(HostWeightHandler, self).__init__(BaseHostWeigher, namespace)