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

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)
@@ -247,6 +251,21 @@ class HKDevice:
             _LOGGER.debug("HomeKit connection not polling any characteristics.")
             return
 
+        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
+
+        if self._polling_lock_warned:
+            _LOGGER.info(
+                "HomeKit controller no longer detecting back pressure - not skipping poll"
+            )
+            self._polling_lock_warned = False
+
+        async with self._polling_lock:
             _LOGGER.debug("Starting HomeKit controller update")
 
             try: