fix(StreamEngine): graceful shutdown must wait for all events to be processed before Streams are stopped. Related to #162

Author: marcosschroh

kstreams/streams.py

@@ -103,6 +103,7 @@ def __init__(
         self.name = name or str(uuid.uuid4())
         self.deserializer = deserializer
         self.running = False
+        self.is_processing = asyncio.Lock()
         self.initial_offsets = initial_offsets
         self.seeked_initial_offsets = False
         self.rebalance_listener = rebalance_listener
@@ -121,15 +122,18 @@ def _create_consumer(self) -> Consumer:
         return self.consumer_class(**config)
 
     async def stop(self) -> None:
-        if not self.running:
-            return None
-
-        if self.consumer is not None:
-            await self.consumer.stop()
+        if self.running:
+            # Don't run anymore to prevent new events comming
             self.running = False
 
-        if self._consumer_task is not None:
-            self._consumer_task.cancel()
+            async with self.is_processing:
+                # Only enter this block when all the events have been
+                # proccessed in the middleware chain
+                if self.consumer is not None:
+                    await self.consumer.stop()
+
+                if self._consumer_task is not None:
+                    self._consumer_task.cancel()
 
     async def _subscribe(self) -> None:
         # Always create a consumer on stream.start
@@ -141,7 +145,6 @@ async def _subscribe(self) -> None:
             self.consumer.subscribe(
                 topics=self.topics, listener=self.rebalance_listener
             )
-            self.running = True
 
     async def commit(
         self, offsets: typing.Optional[typing.Dict[TopicPartition, int]] = None
@@ -206,6 +209,7 @@ async def start(self) -> None:
             return None
 
         await self._subscribe()
+        self.running = True
 
         if self.udf_handler.type == UDFType.NO_TYPING:
             # normal use case
@@ -236,9 +240,10 @@ async def func_wrapper(self, func: typing.Awaitable) -> None:
             logger.exception(f"CRASHED Stream!!! Task {self._consumer_task} \n\n {e}")
 
     async def func_wrapper_with_typing(self) -> None:
-        while True:
+        while self.running:
             cr = await self.getone()
-            await self.func(cr)
+            async with self.is_processing:
+                await self.func(cr)
 
     def seek_to_initial_offsets(self) -> None:
         if not self.seeked_initial_offsets and self.consumer is not None:

kstreams/test_utils/test_utils.py

@@ -17,8 +17,7 @@ class TestMonitor(PrometheusMonitor):
     __test__ = False
 
     def start(self, *args, **kwargs) -> None:
-        print("herte....")
-        # ...
+        ...
 
     async def stop(self, *args, **kwargs) -> None:
         ...

tests/test_stream_engine.py

@@ -264,6 +264,39 @@ async def stream(_):
             Consumer.stop.assert_awaited()
 
 
+@pytest.mark.asyncio
+async def test_wait_for_streams_before_stop(
+    stream_engine: StreamEngine, consumer_record_factory: Callable[..., ConsumerRecord]
+):
+    topic = "local--hello-kpn"
+    value = b"Hello world"
+    save_to_db = mock.AsyncMock()
+
+    async def getone(_):
+        return consumer_record_factory(value=value)
+
+    @stream_engine.stream(topic)
+    async def stream(cr: ConsumerRecord):
+        # Use 5 seconds sleep to simulate a super slow event processing
+        await asyncio.sleep(5)
+        await save_to_db(cr.value)
+
+    with mock.patch.multiple(
+        Consumer,
+        start=mock.DEFAULT,
+        stop=mock.DEFAULT,
+        getone=getone,
+    ), mock.patch.multiple(Producer, start=mock.DEFAULT, stop=mock.DEFAULT):
+        await stream_engine.start()
+        await asyncio.sleep(0)  # Allow stream coroutine to run once
+
+        # stop engine immediately, this should not break the streams
+        # and it should wait until the event is processed.
+        await stream_engine.stop()
+        Consumer.stop.assert_awaited()
+        save_to_db.assert_awaited_once_with(value)
+
+
 @pytest.mark.asyncio
 async def test_recreate_consumer_on_re_start_stream(stream_engine: StreamEngine):
     with mock.patch("kstreams.clients.aiokafka.AIOKafkaConsumer.start"):