use stevedore to load util plugins

Importing pkg_resources has a side-effect of scanning all of the
installed python modules looking for entrypoints to build an in-memory
cache. Stevedore will be adding an on-disk cache to speed that process
up, which should provide significant performance benefits for client
applications such as python-openstackclient. This change introduces
stevedore to replace pkg_resources.

Change-Id: I66decf6d5a4f79ddaa6617737e9334a56dbbbad4
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

2 files changed, 12 insertions, 6 deletions

diff --git a/cinderclient/utils.py b/cinderclient/utils.py
index 28c458d..681a2d4 100644
--- a/cinderclient/utils.py
+++ b/cinderclient/utils.py
@@ -17,13 +17,13 @@ from __future__ import print_function
 import collections
 
 import os
-import pkg_resources
 import sys
 import uuid
 
 import prettytable
 import six
 from six.moves.urllib import parse
+import stevedore
 
 from cinderclient import exceptions
 from oslo_utils import encodeutils
@@ -332,11 +332,16 @@ def safe_issubclass(*args):
 
 def _load_entry_point(ep_name, name=None):
     """Try to load the entry point ep_name that matches name."""
-    for ep in pkg_resources.iter_entry_points(ep_name, name=name):
-        try:
-            return ep.load()
-        except (ImportError, pkg_resources.UnknownExtra, AttributeError):
-            continue
+    mgr = stevedore.NamedExtensionManager(
+        namespace=ep_name,
+        names=[name],
+        # Ignore errors on load
+        on_load_failure_callback=lambda mgr, entry_point, error: None,
+    )
+    try:
+        return mgr[name].plugin
+    except KeyError:
+        pass
 
 
 def get_function_name(func):
diff --git a/requirements.txt b/requirements.txt
index fef5e1e..f6567f4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,3 +9,4 @@ six>=1.10.0 # MIT
 oslo.i18n>=3.15.3 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
 requests!=2.20.0,>=2.14.2  # Apache-2.0
+stevedore>=1.20.0 # Apache-2.0