Reduce event loop overhead for listeners that already queue (#71364)

Co-authored-by: Paulus Schoutsen <paulus@home-assistant.io>

homeassistant/components/recorder/core.py

@@ -237,7 +237,9 @@ class Recorder(threading.Thread):
     def async_initialize(self) -> None:
         """Initialize the recorder."""
         self._event_listener = self.hass.bus.async_listen(
-            MATCH_ALL, self.event_listener, event_filter=self._async_event_filter
+            MATCH_ALL,
+            self.event_listener,
+            run_immediately=True,
         )
         self._queue_watcher = async_track_time_interval(
             self.hass, self._async_check_queue, timedelta(minutes=10)
@@ -916,6 +918,7 @@ class Recorder(threading.Thread):
     @callback
     def event_listener(self, event: Event) -> None:
         """Listen for new events and put them in the process queue."""
+        if self._async_event_filter(event):
             self.queue_task(EventTask(event))
 
     def block_till_done(self) -> None:

homeassistant/components/websocket_api/auth.py

@@ -56,7 +56,7 @@ class AuthPhase:
         self,
         logger: WebSocketAdapter,
         hass: HomeAssistant,
-        send_message: Callable[[str | dict[str, Any]], None],
+        send_message: Callable[[str | dict[str, Any] | Callable[[], str]], None],
         cancel_ws: CALLBACK_TYPE,
         request: Request,
     ) -> None:

homeassistant/components/websocket_api/commands.py

@@ -105,17 +105,21 @@ def handle_subscribe_events(
             ):
                 return
 
-            connection.send_message(messages.cached_event_message(msg["id"], event))
+            connection.send_message(
+                lambda: messages.cached_event_message(msg["id"], event)
+            )
 
     else:
 
         @callback
         def forward_events(event: Event) -> None:
             """Forward events to websocket."""
-            connection.send_message(messages.cached_event_message(msg["id"], event))
+            connection.send_message(
+                lambda: messages.cached_event_message(msg["id"], event)
+            )
 
     connection.subscriptions[msg["id"]] = hass.bus.async_listen(
-        event_type, forward_events
+        event_type, forward_events, run_immediately=True
     )
 
     connection.send_result(msg["id"])
@@ -286,14 +290,16 @@ def handle_subscribe_entities(
         if entity_ids and event.data["entity_id"] not in entity_ids:
             return
 
-        connection.send_message(messages.cached_state_diff_message(msg["id"], event))
+        connection.send_message(
+            lambda: messages.cached_state_diff_message(msg["id"], event)
+        )
 
     # We must never await between sending the states and listening for
     # state changed events or we will introduce a race condition
     # where some states are missed
     states = _async_get_allowed_states(hass, connection)
     connection.subscriptions[msg["id"]] = hass.bus.async_listen(
-        "state_changed", forward_entity_changes
+        EVENT_STATE_CHANGED, forward_entity_changes, run_immediately=True
     )
     connection.send_result(msg["id"])
     data: dict[str, dict[str, dict]] = {

homeassistant/components/websocket_api/connection.py

@@ -30,7 +30,7 @@ class ActiveConnection:
         self,
         logger: WebSocketAdapter,
         hass: HomeAssistant,
-        send_message: Callable[[str | dict[str, Any]], None],
+        send_message: Callable[[str | dict[str, Any] | Callable[[], str]], None],
         user: User,
         refresh_token: RefreshToken,
     ) -> None:

homeassistant/components/websocket_api/http.py

@@ -72,9 +72,13 @@ class WebSocketHandler:
         # Exceptions if Socket disconnected or cancelled by connection handler
         with suppress(RuntimeError, ConnectionResetError, *CANCELLATION_ERRORS):
             while not self.wsock.closed:
-                if (message := await self._to_write.get()) is None:
+                if (process := await self._to_write.get()) is None:
                     break
 
+                if not isinstance(process, str):
+                    message: str = process()
+                else:
+                    message = process
                 self._logger.debug("Sending %s", message)
                 await self.wsock.send_str(message)
 
@@ -84,14 +88,14 @@ class WebSocketHandler:
             self._peak_checker_unsub = None
 
     @callback
-    def _send_message(self, message: str | dict[str, Any]) -> None:
+    def _send_message(self, message: str | dict[str, Any] | Callable[[], str]) -> None:
         """Send a message to the client.
 
         Closes connection if the client is not reading the messages.
 
         Async friendly.
         """
-        if not isinstance(message, str):
+        if isinstance(message, dict):
             message = message_to_json(message)
 
         try:

homeassistant/core.py

@@ -778,6 +778,7 @@ class _FilterableJob(NamedTuple):
 
     job: HassJob[None | Awaitable[None]]
     event_filter: Callable[[Event], bool] | None
+    run_immediately: bool
 
 
 class EventBus:
@@ -845,7 +846,7 @@ class EventBus:
         if not listeners:
             return
 
-        for job, event_filter in listeners:
+        for job, event_filter, run_immediately in listeners:
             if event_filter is not None:
                 try:
                     if not event_filter(event):
@@ -853,6 +854,12 @@ class EventBus:
                 except Exception:  # pylint: disable=broad-except
                     _LOGGER.exception("Error in event filter")
                     continue
+            if run_immediately:
+                try:
+                    job.target(event)
+                except Exception:  # pylint: disable=broad-except
+                    _LOGGER.exception("Error running job: %s", job)
+            else:
                 self._hass.async_add_hass_job(job, event)
 
     def listen(
@@ -881,6 +888,7 @@ class EventBus:
         event_type: str,
         listener: Callable[[Event], None | Awaitable[None]],
         event_filter: Callable[[Event], bool] | None = None,
+        run_immediately: bool = False,
     ) -> CALLBACK_TYPE:
         """Listen for all events or events of a specific type.
 
@@ -891,12 +899,18 @@ class EventBus:
         @callback that returns a boolean value, determines if the
         listener callable should run.
 
+        If run_immediately is passed, the callback will be run
+        right away instead of using call_soon. Only use this if
+        the callback results in scheduling another task.
+
         This method must be run in the event loop.
         """
         if event_filter is not None and not is_callback(event_filter):
             raise HomeAssistantError(f"Event filter {event_filter} is not a callback")
+        if run_immediately and not is_callback(listener):
+            raise HomeAssistantError(f"Event listener {listener} is not a callback")
         return self._async_listen_filterable_job(
-            event_type, _FilterableJob(HassJob(listener), event_filter)
+            event_type, _FilterableJob(HassJob(listener), event_filter, run_immediately)
         )
 
     @callback
@@ -966,7 +980,7 @@ class EventBus:
             _onetime_listener, listener, ("__name__", "__qualname__", "__module__"), []
         )
 
-        filterable_job = _FilterableJob(HassJob(_onetime_listener), None)
+        filterable_job = _FilterableJob(HassJob(_onetime_listener), None, False)
 
         return self._async_listen_filterable_job(event_type, filterable_job)
 

tests/test_core.py

@@ -442,6 +442,24 @@ async def test_eventbus_filtered_listener(hass):
     unsub()
 
 
+async def test_eventbus_run_immediately(hass):
+    """Test we can call events immediately."""
+    calls = []
+
+    @ha.callback
+    def listener(event):
+        """Mock listener."""
+        calls.append(event)
+
+    unsub = hass.bus.async_listen("test", listener, run_immediately=True)
+
+    hass.bus.async_fire("test", {"event": True})
+    # No async_block_till_done here
+    assert len(calls) == 1
+
+    unsub()
+
+
 async def test_eventbus_unsubscribe_listener(hass):
     """Test unsubscribe listener from returned function."""
     calls = []