Add a sleep in Jupyter Backend poll loop (#37)

* Add a sleep in Jupyter Backend poll loop

* docstring

* make the sleep time a class attribute so we can change it in PA

* fix docstring

CHANGELOG.md

@@ -17,6 +17,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Use `managed_service_fixtures` for Redis tests
 - `WebsocketManager` backend uses vanilla `logging` instead of `structlog`, remove need for `structlog` dependency once `managed-service-fixtures` also drops it
+- `JupyterBackend` introduce a short sleep in its poll loop while investigating 100% CPU usage
 
 ## [0.2.2] - 2022-07-28
 ### Changed

sending/backends/jupyter.py

@@ -1,7 +1,9 @@
+import asyncio
 from queue import Empty
 from typing import Optional, Union
 
 from jupyter_client import AsyncKernelClient
+from jupyter_client.channels import ZMQSocketChannel
 from zmq import NOBLOCK, Event, Socket, SocketOption, pyzmq_version, zmq_version
 from zmq.asyncio import Context
 from zmq.utils.monitor import recv_monitor_message
@@ -11,11 +13,18 @@
 
 
 class JupyterKernelManager(AbstractPubSubManager):
-    def __init__(self, connection_info: dict, *, max_message_size: int = None):
+    def __init__(
+        self,
+        connection_info: dict,
+        *,
+        max_message_size: int = None,
+        sleep_between_polls: float = 0.005,
+    ):
         super().__init__()
         self.connection_info = connection_info
         self._monitor_sockets_for_topic: dict[str, Socket] = {}
         self.max_message_size = max_message_size
+        self.sleep_between_polls = sleep_between_polls
 
     async def initialize(
         self, *, queue_size=0, inbound_workers=1, outbound_workers=1, poll_workers=1
@@ -93,7 +102,7 @@ def _cycle_socket(self, topic):
 
     async def _poll(self):
         for topic_name in self.subscribed_topics:
-            channel_obj = getattr(self._client, f"{topic_name}_channel")
+            channel_obj: ZMQSocketChannel = getattr(self._client, f"{topic_name}_channel")
 
             while True:
                 try:
@@ -117,3 +126,18 @@ async def _poll(self):
             # when it violates some constraint such as the max message size.
             logger.info(f"ZMQ disconnected for topic '{topic}', cycling socket")
             self._cycle_socket(topic)
+
+    async def _poll_loop(self):
+        """
+        Override base Manager _poll_loop to switch the final asyncio.sleep from 0 to
+        something more than that (definable at init or after instantiation, default 0.005).
+        While observing JupyterManager in real world, containers are using 100% CPU.
+        Possibly due to this loop being too aggressive?
+        """
+        while True:
+            try:
+                await self._poll()
+            except Exception:
+                logger.exception("Uncaught exception encountered while polling backend")
+            finally:
+                await asyncio.sleep(self.sleep_between_polls)