eventletutils: Fix behavior discrepency when reusing Events

The threading.Event object allows calling set() multiple times, but
the eventlet.Event object only permits send() to be called once,
before a reset() is required to reuse the Event.

Calling eventletutils.Event.set() multiple times triggers an
AssertionError from eventlet.Event.  This change resets the underlying
eventlet.Event if the set() method had already been called previously,
and ensures the eventletutils.Event behaves the same as the
threading.Event.

Change-Id: If761b237266bbfe7e65c56e152074b5d1ccac74b

2 files changed, 13 insertions, 2 deletions

diff --git a/oslo_utils/eventletutils.py b/oslo_utils/eventletutils.py
index f5bca51..46d9ba7 100644
--- a/oslo_utils/eventletutils.py
+++ b/oslo_utils/eventletutils.py
@@ -159,6 +159,9 @@ class _Event(object):
     isSet = is_set
 
     def set(self):
+        if self._set:
+            self._event.reset()
+
         self._set = True
         self._event.send(True)
 
diff --git a/oslo_utils/tests/test_eventletutils.py b/oslo_utils/tests/test_eventletutils.py
index e5765c7..8e71e81 100644
--- a/oslo_utils/tests/test_eventletutils.py
+++ b/oslo_utils/tests/test_eventletutils.py
@@ -123,8 +123,8 @@ class EventletUtilsTest(test_base.BaseTestCase):
                           eventletutils.warn_eventlet_not_patched,
                           ['blah.blah'])
 
-    @mock.patch('oslo_utils.eventletutils._Event.clear')
-    def test_event_api_compat(self, mock_clear):
+    @mock.patch('oslo_utils.eventletutils._eventlet')
+    def test_event_api_compat(self, mock_eventlet):
         with mock.patch('oslo_utils.eventletutils.is_monkey_patched',
                         return_value=True):
             e_event = eventletutils.Event()
@@ -142,3 +142,11 @@ class EventletUtilsTest(test_base.BaseTestCase):
 
         for method in public_methods:
             self.assertTrue(hasattr(e_event, method))
+
+        # Ensure set() allows multiple invocations, same as in
+        # threading implementation.  Must call reset on underlying
+        # Event before reusing it
+        e_event.set()
+        self.assertEqual(0, mock_eventlet.event.Event().reset.call_count)
+        e_event.set()
+        self.assertEqual(1, mock_eventlet.event.Event().reset.call_count)