fix: Prometheus scrape metrics task fixed in order to have a proper s…

…hutdown (#124)

The monitor shutdown will wait until the scraping Task is done rather than canceling it.
Parameter metrics_scrape_time added.

kstreams/engine.py

@@ -139,9 +139,9 @@ async def start(self) -> None:
         self.monitor.start()
 
     async def stop(self) -> None:
-        await self.stop_streams()
-        await self.stop_producer()
         await self.monitor.stop()
+        await self.stop_producer()
+        await self.stop_streams()
 
     async def stop_producer(self):
         logger.info("Waiting Producer to STOP....")

kstreams/prometheus/monitor.py

@@ -1,6 +1,6 @@
 import asyncio
 import logging
-from typing import DefaultDict, Dict, Optional, TypeVar
+from typing import DefaultDict, Dict, List, Optional, TypeVar
 
 from prometheus_client import Gauge
 
@@ -17,6 +17,10 @@
 class PrometheusMonitor:
     """
     Metrics monitor to keep track of Producers and Consumers.
+
+     Attributes:
+        metrics_scrape_time float: Amount of seconds that the monitor
+            will wait until next scrape iteration
     """
 
     # Producer metrics
@@ -51,23 +55,26 @@ class PrometheusMonitor:
         ["topic", "partition", "consumer_group"],
     )
 
-    def __init__(self):
+    def __init__(self, metrics_scrape_time: float = 3):
+        self.metrics_scrape_time = metrics_scrape_time
+        self.running = False
         self._producer = None
-        self._streams = []
+        self._streams: List[Stream] = []
         self._task: Optional[asyncio.Task] = None
 
     def start(self) -> None:
         logger.info("Starting Prometheus metrics...")
+        self.running = True
         self._task = asyncio.create_task(self._metrics_task())
 
     async def stop(self) -> None:
         logger.info("Stoping Prometheus metrics...")
-        if self._task is not None:
-            self._task.cancel()
+        self.running = False
 
-            # we need to make sure that the task is cancelled
+        if self._task is not None:
+            # we need to make sure that the task is `done`
             # to clean up properly
-            while not self._task.cancelled():
+            while not self._task.done():
                 await asyncio.sleep(0.1)
 
         self._clean_consumer_metrics()
@@ -214,10 +221,13 @@ async def generate_consumer_metrics(self, consumer: ConsumerType):
     async def _metrics_task(self) -> None:
         """
         Asyncio Task that runs in `backgroud` to generate
-        consumer metrics
+        consumer metrics.
+
+        When self.running is False the task will finish and it
+        will be safe to stop consumers and producers.
         """
-        while True:
-            await asyncio.sleep(3)
+        while self.running:
+            await asyncio.sleep(self.metrics_scrape_time)
             for stream in self._streams:
                 if stream.consumer is not None:
                     try:

kstreams/streams.py

@@ -99,7 +99,7 @@ def __init__(
         self.func = func
         self.backend = backend
         self.consumer_class = consumer_class
-        self.consumer: Optional[Type[ConsumerType]] = None
+        self.consumer: Optional[ConsumerType] = None
         self.config = config or {}
         self._consumer_task: Optional[asyncio.Task] = None
         self.name = name or str(uuid.uuid4())
@@ -115,7 +115,7 @@ def __init__(
         # so we always create a list and then we expand it with *topics
         self.topics = [topics] if isinstance(topics, str) else topics
 
-    def _create_consumer(self) -> Type[ConsumerType]:
+    def _create_consumer(self) -> ConsumerType:
         if self.backend is None:
             raise BackendNotSet("A backend has not been set for this stream")
         config = {**self.backend.dict(), **self.config}
@@ -135,10 +135,14 @@ async def stop(self) -> None:
     async def _subscribe(self) -> None:
         # Always create a consumer on stream.start
         self.consumer = self._create_consumer()
-        await self.consumer.start()
-        self.running = True
 
-        self.consumer.subscribe(topics=self.topics, listener=self.rebalance_listener)
+        # add the chech tp avoid `mypy` complains
+        if self.consumer is not None:
+            await self.consumer.start()
+            self.consumer.subscribe(
+                topics=self.topics, listener=self.rebalance_listener
+            )
+            self.running = True
 
     async def commit(self, offsets: Optional[Dict[TopicPartition, int]] = None):
         await self.consumer.commit(offsets=offsets)  # type: ignore