Delay Gerrit events by 5s

When querying a change immediately after a patchset upload, Gerrit
may return incorrect data about dependent changes.  In order to
avoid this, ensure at least 5 seconds have elapsed before delivering
any Gerrit events to Zuul.

Change-Id: I95c459f52562556ca1722878e32388d51033e86c

3 files changed, 14 insertions, 4 deletions

diff --git a/tests/base.py b/tests/base.py
index 08b3cab41..cd87b243a 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -396,7 +396,7 @@ class FakeGerrit(object):
         return c
 
     def addEvent(self, data):
-        return self.event_queue.put(data)
+        return self.event_queue.put((time.time(), data))
 
     def getEvent(self):
         return self.event_queue.get()
@@ -479,6 +479,7 @@ class FakeGerritTrigger(zuul.trigger.gerrit.Gerrit):
     def __init__(self, upstream_root, *args):
         super(FakeGerritTrigger, self).__init__(*args)
         self.upstream_root = upstream_root
+        self.gerrit_connector.delay = 0.0
 
     def getGitUrl(self, project):
         return os.path.join(self.upstream_root, project.name)
diff --git a/zuul/lib/gerrit.py b/zuul/lib/gerrit.py
index 9aeff3df8..6c7906bd2 100644
--- a/zuul/lib/gerrit.py
+++ b/zuul/lib/gerrit.py
@@ -39,7 +39,7 @@ class GerritWatcher(threading.Thread):
         data = json.loads(l)
         self.log.debug("Received data from Gerrit event stream: \n%s" %
                        pprint.pformat(data))
-        self.gerrit.addEvent(data)
+        self.gerrit.addEvent((time.time(), data))
 
     def _listen(self, stdout, stderr):
         poll = select.poll()
diff --git a/zuul/trigger/gerrit.py b/zuul/trigger/gerrit.py
index 7d970ad1c..a99db4d1f 100644
--- a/zuul/trigger/gerrit.py
+++ b/zuul/trigger/gerrit.py
@@ -26,6 +26,7 @@ class GerritEventConnector(threading.Thread):
     """Move events from Gerrit to the scheduler."""
 
     log = logging.getLogger("zuul.GerritEventConnector")
+    delay = 5.0
 
     def __init__(self, gerrit, sched, trigger):
         super(GerritEventConnector, self).__init__()
@@ -37,12 +38,20 @@ class GerritEventConnector(threading.Thread):
 
     def stop(self):
         self._stopped = True
-        self.gerrit.addEvent(None)
+        self.gerrit.addEvent((None, None))
 
     def _handleEvent(self):
-        data = self.gerrit.getEvent()
+        ts, data = self.gerrit.getEvent()
         if self._stopped:
             return
+        # Gerrit can produce inconsistent data immediately after an
+        # event, So ensure that we do not deliver the event to Zuul
+        # until at least a certain amount of time has passed.  Note
+        # that if we receive several events in succession, we will
+        # only need to delay for the first event.  In essence, Zuul
+        # should always be a constant number of seconds behind Gerrit.
+        now = time.time()
+        time.sleep(max((ts + self.delay) - now, 0.0))
         event = TriggerEvent()
         event.type = data.get('type')
         event.trigger_name = self.trigger.name