Fix circular dependency of certificate_manager module

The certificate_manager module had a circular dependency that made it
problematic to use for certain versions of the python interpreter.
This was because we were initializing a singleton EVENT_PLUGIN_MANAGER
that in turn loaded the plugins; The problem was that the plugins
imported certificate_manger themselves and this caused the circular
dependency. So instead of creating that class in the module, I
created a function that should be called instead.

Closes-Bug: #1570356
Change-Id: I9cdb7c3ecc9c275ee561363f6ce13248259f88d0

barbican/plugin/interface/certificate_manager.py

@@ -105,6 +105,10 @@ INFO_INTERMEDIATES = "intermediates"
 INFO_EXPIRATION = "expiration"
 
 
+# Singleton to avoid loading the CertificateEventManager plugins more than once
+_EVENT_PLUGIN_MANAGER = None
+
+
 class CertificateRequestType(object):
     """Constants to define the certificate request type."""
     CUSTOM_REQUEST = "custom"
@@ -702,8 +706,8 @@ class _CertificateEventPluginManager(named.NamedExtensionManager,
 
     Each time this class is initialized it will load a new instance
     of each enabled plugin. This is undesirable, so rather than initializing a
-    new instance of this class use the EVENT_PLUGIN_MANAGER at the module
-    level.
+    new instance of this class use the get_event_plugin_manager function
+    at the module level.
     """
     def __init__(self, conf=CONF, invoke_args=(), invoke_kwargs={}):
         super(_CertificateEventPluginManager, self).__init__(
@@ -750,4 +754,9 @@ class _CertificateEventPluginManager(named.NamedExtensionManager,
             getattr(plugin, method)(*args, **kwargs)
 
 
-EVENT_PLUGIN_MANAGER = _CertificateEventPluginManager()
+def get_event_plugin_manager():
+    global _EVENT_PLUGIN_MANAGER
+    if _EVENT_PLUGIN_MANAGER:
+        return _EVENT_PLUGIN_MANAGER
+    _EVENT_PLUGIN_MANAGER = _CertificateEventPluginManager()
+    return _EVENT_PLUGIN_MANAGER

barbican/tasks/certificate_resources.py

@@ -516,7 +516,7 @@ def _get_container_from_order_meta(order_model, project_model):
 
 def _notify_ca_unavailable(order_model, result):
     """Notify observer(s) that the CA was unavailable at this time."""
-    cert.EVENT_PLUGIN_MANAGER.notify_ca_is_unavailable(
+    cert.get_event_plugin_manager().notify_ca_is_unavailable(
         order_model.project_id,
         hrefs.convert_order_to_href(order_model.id),
         result.status_message,

barbican/tests/plugin/interface/test_certificate_manager.py

@@ -38,7 +38,7 @@ class WhenTestingCertificateEventPluginManager(testtools.TestCase):
         self.plugin_name = common_utils.generate_fullname_for(
             self.plugin_returned)
         self.plugin_loaded = mock.MagicMock(obj=self.plugin_returned)
-        self.manager = cm.EVENT_PLUGIN_MANAGER
+        self.manager = cm.get_event_plugin_manager()
         self.manager.extensions = [self.plugin_loaded]
 
     def test_get_plugin_by_name(self):

barbican/tests/tasks/test_certificate_resources.py

@@ -395,7 +395,7 @@ class BaseCertificateRequestsTestCase(database_utils.RepositoryTestCase):
         """Mock the certificate event plugin manager."""
         self.cert_event_plugin_patcher = mock.patch(
             'barbican.plugin.interface.certificate_manager'
-            '.EVENT_PLUGIN_MANAGER'
+            '._EVENT_PLUGIN_MANAGER'
         )
         self.cert_event_plugin_patcher.start()
 
@@ -690,7 +690,7 @@ class WhenIssuingCertificateRequests(BaseCertificateRequestsTestCase):
 
         self._verify_issue_certificate_plugins_called()
 
-        epm = self.cert_event_plugin_patcher.target.EVENT_PLUGIN_MANAGER
+        epm = self.cert_event_plugin_patcher.target._EVENT_PLUGIN_MANAGER
         epm.notify_ca_is_unavailable.assert_called_once_with(
             self.project.id,
             order_ref,
@@ -775,7 +775,7 @@ class WhenCheckingCertificateRequests(BaseCertificateRequestsTestCase):
 
         self._verify_check_certificate_plugins_called()
 
-        epm = self.cert_event_plugin_patcher.target.EVENT_PLUGIN_MANAGER
+        epm = self.cert_event_plugin_patcher.target._EVENT_PLUGIN_MANAGER
         epm.notify_ca_is_unavailable.assert_called_once_with(
             self.project.id,
             order_ref,