Fix reset/start methods on AgentStatusCheckWorker

This worker would fail to start again if stop() or reset()
was called on it because of some bad conditional logic. This
doesn't appear to impact the current in-tree use case but
it should behave correctly.

Closes-Bug: #1641788
Change-Id: Id6334c1ef6c99bd112ada31e8fe3746d7e035356

neutron/db/agentschedulers_db.py

@@ -86,8 +86,8 @@ class AgentStatusCheckWorker(neutron_worker.NeutronWorker):
         super(AgentStatusCheckWorker, self).start()
         if self._loop is None:
             self._loop = loopingcall.FixedIntervalLoopingCall(self._check_func)
-            self._loop.start(interval=self._interval,
-                             initial_delay=self._initial_delay)
+        self._loop.start(interval=self._interval,
+                         initial_delay=self._initial_delay)
 
     def wait(self):
         if self._loop is not None:
@@ -98,10 +98,9 @@ class AgentStatusCheckWorker(neutron_worker.NeutronWorker):
             self._loop.stop()
 
     def reset(self):
-        if self._loop is not None:
-            self.stop()
-            self.wait()
-            self.start()
+        self.stop()
+        self.wait()
+        self.start()
 
 
 class AgentSchedulerDbMixin(agents_db.AgentDbMixin):

neutron/tests/unit/db/test_agentschedulers_db.py

@@ -29,6 +29,7 @@ from neutron.api.rpc.handlers import dhcp_rpc
 from neutron.api.rpc.handlers import l3_rpc
 from neutron.api.v2 import attributes
 from neutron.common import constants as n_const
+from neutron.common import utils
 from neutron import context
 from neutron.db import agents_db
 from neutron.db import agentschedulers_db
@@ -39,6 +40,7 @@ from neutron.extensions import dhcpagentscheduler
 from neutron.extensions import l3agentscheduler
 from neutron import manager
 from neutron.plugins.common import constants as service_constants
+from neutron.tests import base
 from neutron.tests.common import helpers
 from neutron.tests import fake_notifier
 from neutron.tests import tools
@@ -1451,6 +1453,31 @@ class OvsDhcpAgentNotifierTestCase(test_agent.AgentDBTestMixIn,
         self.assertTrue(self._is_schedule_network_called(device_id))
 
 
+class AgentStatusCheckWorkerTestCase(base.BaseTestCase):
+
+    def test_agent_worker_lifecycle(self):
+        check_function = mock.Mock()
+        worker = agentschedulers_db.AgentStatusCheckWorker(
+            check_function, interval=1, initial_delay=1)
+        self.addCleanup(worker.stop)
+        worker.wait()
+        self.assertFalse(check_function.called)
+        worker.start()
+        utils.wait_until_true(
+            lambda: check_function.called,
+            timeout=5,
+            exception=RuntimeError("check_function not called"))
+        worker.stop()
+        check_function.reset_mock()
+        worker.wait()
+        self.assertFalse(check_function.called)
+        worker.reset()
+        utils.wait_until_true(
+            lambda: check_function.called,
+            timeout=5,
+            exception=RuntimeError("check_function not called"))
+
+
 class OvsL3AgentNotifierTestCase(test_l3.L3NatTestCaseMixin,
                                  test_agent.AgentDBTestMixIn,
                                  AgentSchedulerTestMixIn,