rehome utils: synchronized decorator and load_class_by_alias_or_classname

This patch rehomes the neutron common utils:
- load_class_by_alias_or_classname() function.
- synchronized decorator.

These utils are used by subprojects [1] and will
also be used as part of rehoming the logic in neutron's
manager module.

[1] http://codesearch.openstack.org/?q=load_class_by_alias_or_classname

Change-Id: I62958e30695663797d79ed6bd1260edbb46a1bf4

neutron_lib/tests/unit/utils/test_runtime.py

@@ -0,0 +1,53 @@
+# 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 mock
+
+from neutron_lib.tests import _base as base
+from neutron_lib.utils import runtime
+
+
+class _DummyDriver(object):
+    driver = mock.sentinel.dummy_driver
+
+
+class TestRunTime(base.BaseTestCase):
+
+    @mock.patch.object(runtime, 'LOG')
+    def test_load_class_by_alias_or_classname_no_name(self, mock_log):
+        self.assertRaises(
+            ImportError,
+            runtime.load_class_by_alias_or_classname, 'ns', None)
+
+    @mock.patch.object(runtime.driver, 'DriverManager',
+                       return_value=_DummyDriver)
+    @mock.patch.object(runtime, 'LOG')
+    def test_load_class_by_alias_or_classname_dummy_driver(
+            self, mock_log, mock_driver):
+        self.assertEqual(_DummyDriver.driver,
+                         runtime.load_class_by_alias_or_classname('ns', 'n'))
+
+    @mock.patch.object(runtime, 'LOG')
+    def test_load_class_by_alias_or_classname_bad_classname(self, mock_log):
+        self.assertRaises(
+            ImportError,
+            runtime.load_class_by_alias_or_classname, 'ns', '_NoClass')
+
+    @mock.patch.object(runtime.importutils, 'import_class',
+                       return_value=mock.sentinel.dummy_class)
+    @mock.patch.object(runtime, 'LOG')
+    def test_load_class_by_alias_or_classname_with_classname(
+            self, mock_log, mock_import):
+        self.assertEqual(
+            mock.sentinel.dummy_class,
+            runtime.load_class_by_alias_or_classname('ns', 'n'))

neutron_lib/utils/runtime.py

@@ -0,0 +1,59 @@
+# 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 sys
+
+from oslo_concurrency import lockutils
+from oslo_log import log as logging
+from oslo_utils import importutils
+from stevedore import driver
+
+from neutron_lib._i18n import _
+
+LOG = logging.getLogger(__name__)
+SYNCHRONIZED_PREFIX = 'neutron-'
+
+
+# common synchronization decorator
+synchronized = lockutils.synchronized_with_prefix(SYNCHRONIZED_PREFIX)
+
+
+def load_class_by_alias_or_classname(namespace, name):
+    """Load a class using stevedore alias or the class name.
+
+    :param namespace: The namespace where the alias is defined.
+    :param name: The alias or class name of the class to be loaded.
+    :returns: Class if it can be loaded.
+    :raises ImportError if class cannot be loaded.
+    """
+
+    if not name:
+        LOG.error("Alias or class name is not set")
+        raise ImportError(_("Class not found."))
+    try:
+        # Try to resolve class by alias
+        mgr = driver.DriverManager(
+            namespace, name, warn_on_missing_entrypoint=False)
+        class_to_load = mgr.driver
+    except RuntimeError:
+        e1_info = sys.exc_info()
+        # Fallback to class name
+        try:
+            class_to_load = importutils.import_class(name)
+        except (ImportError, ValueError):
+            LOG.error("Error loading class by alias",
+                      exc_info=e1_info)
+            LOG.error("Error loading class by class name",
+                      exc_info=True)
+            raise ImportError(_("Class not found."))
+    return class_to_load

releasenotes/notes/rehome-runtime-utils-acb4451326cbe4d9.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - The ``load_class_by_alias_or_classname`` function from
+    ``neutron.common.utils`` is now available in ``neutron_lib.utils.runtime``.
+  - The ``synchronized`` decorator from ``neutron.common.utils`` is now
+    available in ``neutron_lib.utils.runtime``.

requirements.txt

@@ -6,6 +6,7 @@ pbr!=2.1.0,>=2.0.0 # Apache-2.0
 
 SQLAlchemy!=1.1.5,!=1.1.6,!=1.1.7,!=1.1.8,>=1.0.10 # MIT
 debtcollector>=1.2.0 # Apache-2.0
+stevedore>=1.20.0 # Apache-2.0
 oslo.concurrency>=3.8.0 # Apache-2.0
 oslo.config>=3.22.0 # Apache-2.0
 oslo.context>=2.12.0 # Apache-2.0