Worker: discard task updates when task is assigned to another worker

The Manager will return a 409 Conflict status for updates to tasks that
have been assigned to another worker. This change prevents the worker
from trying to push these updates indefinitely to the Manager.

packages/flamenco-worker-python/flamenco_worker/upstream_update_queue.py

@@ -126,8 +126,14 @@ class TaskUpdateQueue:
 
             self._log.info('Pushing task update to Manager')
             resp = await self.manager.post(url, json=payload, loop=loop)
-            resp.raise_for_status()
-            self._log.debug('Master accepted pushed update.')
+            if resp.status_code == 409:
+                # The task was assigned to another worker, so we're not allowed to
+                # push updates for it. We have to un-queue this update, as it will
+                # never be accepted.
+                self._log.warning('Task was assigned to another worker, discarding update.')
+            else:
+                resp.raise_for_status()
+                self._log.debug('Master accepted pushed update.')
             self._unqueue(rowid)
 
         if queue_is_empty:

packages/flamenco-worker-python/tests/test_upstream_update_queue.py

@@ -147,3 +147,39 @@ class TaskUpdateQueueTest(AbstractWorkerTest):
         self.assertEqual(received_url, '/push/there')
         self.assertEqual(received_payload, payload)
         self.assertEqual(received_loop, self.asyncio_loop)
+
+    def test_conflict(self):
+        """A 409 Conflict response should discard a queued task update.
+        """
+
+        from mock_responses import JsonResponse, EmptyResponse
+
+        # Try different value types
+        payload = {'key': 'value',
+                   'sub': {'some': 13,
+                           'values': datetime.datetime.now()}}
+
+        tries = 0
+
+        async def push_callback(url, *, json, loop):
+            nonlocal tries
+            tries += 1
+            self.shutdown_future.cancel()
+            return JsonResponse({}, status_code=409)
+
+        self.manager.post.side_effect = push_callback
+
+        self.tuqueue.queue('/push/here', payload, loop=self.asyncio_loop)
+
+        # Run the loop for 2 seconds. This should be enough for 3 retries of 0.3 seconds + handling
+        # the actual payload.
+        self.asyncio_loop.run_until_complete(
+            asyncio.wait_for(
+                self.tuqueue.work(loop=self.asyncio_loop),
+                timeout=2
+            )
+        )
+
+        # There should only be one attempt at delivering this payload.
+        self.assertEqual(1, tries)
+        self.assertEqual([], list(self.tuqueue._queue()))