Avoid calling eventlet.event.Event.reset()

The eventlet maintainers have made it clear that calling reset() on an
Event is not recommended:

715b2ced52

We don't really need to resend the event to wake up threads, because
Event.wait() will return immediately once the event has been sent. So
just rely on the internal _set flag to tell us whether we need to send
the event.

Change-Id: I466aa7cb64308e018598c3bb63a9d0cfbc833adc

oslo_utils/eventletutils.py

@@ -165,11 +165,9 @@ class EventletEvent(object):
     isSet = is_set
 
     def set(self):
-        if self._set:
-            self._event.reset()
-
-        self._set = True
-        self._event.send(True)
+        if not self._set:
+            self._set = True
+            self._event.send(True)
 
     def wait(self, timeout=None):
         with timeutils.StopWatch(timeout) as sw:

oslo_utils/tests/test_eventletutils.py

@@ -146,12 +146,11 @@ class EventletUtilsTest(test_base.BaseTestCase):
             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
+        # threading implementation.
         e_event.set()
-        self.assertEqual(0, mock_eventlet.event.Event().reset.call_count)
+        self.assertTrue(e_event.isSet())
         e_event.set()
-        self.assertEqual(1, mock_eventlet.event.Event().reset.call_count)
+        self.assertTrue(e_event.isSet())
 
     def test_event_no_timeout(self):
         event = eventletutils.EventletEvent()