From 2bd832cd7afa7e48bf4d0fce4d46cef3addbbda1 Mon Sep 17 00:00:00 2001
From: Jc2k <john.carr@unrouted.co.uk>
Date: Sun, 18 Aug 2019 05:14:46 +0100
Subject: [PATCH] Skip homekit_controller polls when system is overloaded and
 still trying to process the previous one (#25968)

* Skip async_update if there are signs of backpressure

* Black

* Only warn once

* Log on recovery

* Formatting fix
---
 .../homekit_controller/connection.py          | 49 +++++++++++++------
 1 file changed, 34 insertions(+), 15 deletions(-)

diff --git a/homeassistant/components/homekit_controller/connection.py b/homeassistant/components/homekit_controller/connection.py
index 8068f26aaa3..1cb2131fb8f 100644
--- a/homeassistant/components/homekit_controller/connection.py
+++ b/homeassistant/components/homekit_controller/connection.py
@@ -103,6 +103,10 @@ class HKDevice:
         # this method.
         self._polling_interval_remover = None
 
+        # Never allow concurrent polling of the same accessory or bridge
+        self._polling_lock = asyncio.Lock()
+        self._polling_lock_warned = False
+
     def add_pollable_characteristics(self, characteristics):
         """Add (aid, iid) pairs that we need to poll."""
         self.pollable_characteristics.extend(characteristics)
@@ -247,25 +251,40 @@ class HKDevice:
             _LOGGER.debug("HomeKit connection not polling any characteristics.")
             return
 
-        _LOGGER.debug("Starting HomeKit controller update")
+        if self._polling_lock.locked():
+            if not self._polling_lock_warned:
+                _LOGGER.warning(
+                    "HomeKit controller update skipped as previous poll still in flight"
+                )
+                self._polling_lock_warned = True
+            return
 
-        try:
-            new_values_dict = await self.get_characteristics(
-                self.pollable_characteristics
+        if self._polling_lock_warned:
+            _LOGGER.info(
+                "HomeKit controller no longer detecting back pressure - not skipping poll"
             )
-        except AccessoryNotFoundError:
-            # Not only did the connection fail, but also the accessory is not
-            # visible on the network.
-            self.async_set_unavailable()
-            return
-        except (AccessoryDisconnectedError, EncryptionError):
-            # Temporary connection failure. Device is still available but our
-            # connection was dropped.
-            return
+            self._polling_lock_warned = False
 
-        self.process_new_events(new_values_dict)
+        async with self._polling_lock:
+            _LOGGER.debug("Starting HomeKit controller update")
 
-        _LOGGER.debug("Finished HomeKit controller update")
+            try:
+                new_values_dict = await self.get_characteristics(
+                    self.pollable_characteristics
+                )
+            except AccessoryNotFoundError:
+                # Not only did the connection fail, but also the accessory is not
+                # visible on the network.
+                self.async_set_unavailable()
+                return
+            except (AccessoryDisconnectedError, EncryptionError):
+                # Temporary connection failure. Device is still available but our
+                # connection was dropped.
+                return
+
+            self.process_new_events(new_values_dict)
+
+            _LOGGER.debug("Finished HomeKit controller update")
 
     def process_new_events(self, new_values_dict):
         """Process events from accessory into HA state."""