Move common libs to libs/common

libs/common/stevedore/hook.py

@@ -0,0 +1,91 @@
+#  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 .named import NamedExtensionManager
+
+
+class HookManager(NamedExtensionManager):
+    """Coordinate execution of multiple extensions using a common name.
+
+    :param namespace: The namespace for the entry points.
+    :type namespace: str
+    :param name: The name of the hooks to load.
+    :type name: str
+    :param invoke_on_load: Boolean controlling whether to invoke the
+        object returned by the entry point after the driver is loaded.
+    :type invoke_on_load: bool
+    :param invoke_args: Positional arguments to pass when invoking
+        the object returned by the entry point. Only used if invoke_on_load
+        is True.
+    :type invoke_args: tuple
+    :param invoke_kwds: Named arguments to pass when invoking
+        the object returned by the entry point. Only used if invoke_on_load
+        is True.
+    :type invoke_kwds: dict
+    :param on_load_failure_callback: Callback function that will be called when
+        a entrypoint can not be loaded. The arguments that will be provided
+        when this is called (when an entrypoint fails to load) are
+        (manager, entrypoint, exception)
+    :type on_load_failure_callback: function
+    :param verify_requirements: Use setuptools to enforce the
+        dependencies of the plugin(s) being loaded. Defaults to False.
+    :type verify_requirements: bool
+    :type on_missing_entrypoints_callback: function
+    :param verify_requirements: Use setuptools to enforce the
+        dependencies of the plugin(s) being loaded. Defaults to False.
+    :param warn_on_missing_entrypoint: Flag to control whether failing
+        to load a plugin is reported via a log mess. Only applies if
+        on_missing_entrypoints_callback is None.
+    :type warn_on_missing_entrypoint: bool
+
+    """
+
+    def __init__(self, namespace, name,
+                 invoke_on_load=False, invoke_args=(), invoke_kwds={},
+                 on_load_failure_callback=None,
+                 verify_requirements=False,
+                 on_missing_entrypoints_callback=None,
+                 # NOTE(dhellmann): This default is different from the
+                 # base class because for hooks it is less likely to
+                 # be an error to have no entry points present.
+                 warn_on_missing_entrypoint=False):
+        super(HookManager, self).__init__(
+            namespace,
+            [name],
+            invoke_on_load=invoke_on_load,
+            invoke_args=invoke_args,
+            invoke_kwds=invoke_kwds,
+            on_load_failure_callback=on_load_failure_callback,
+            on_missing_entrypoints_callback=on_missing_entrypoints_callback,
+            verify_requirements=verify_requirements,
+            warn_on_missing_entrypoint=warn_on_missing_entrypoint,
+        )
+
+    def _init_attributes(self, namespace, names, name_order=False,
+                         propagate_map_exceptions=False,
+                         on_load_failure_callback=None):
+        super(HookManager, self)._init_attributes(
+            namespace, names,
+            propagate_map_exceptions=propagate_map_exceptions,
+            on_load_failure_callback=on_load_failure_callback)
+        self._name = names[0]
+
+    def __getitem__(self, name):
+        """Return the named extensions.
+
+        Accessing a HookManager as a dictionary (``em['name']``)
+        produces a list of the :class:`Extension` instance(s) with the
+        specified name, in the order they would be invoked by map().
+        """
+        if name != self._name:
+            raise KeyError(name)
+        return self.extensions