Prevent parallel reload of automations (#50008)

homeassistant/components/automation/__init__.py

@@ -54,7 +54,10 @@ from homeassistant.helpers.script import (
     Script,
 )
 from homeassistant.helpers.script_variables import ScriptVariables
-from homeassistant.helpers.service import async_register_admin_service
+from homeassistant.helpers.service import (
+    ReloadServiceHelper,
+    async_register_admin_service,
+)
 from homeassistant.helpers.trace import (
     TraceElement,
     script_execution_set,
@@ -253,8 +256,14 @@ async def async_setup(hass, config):
         await _async_process_config(hass, conf, component)
         hass.bus.async_fire(EVENT_AUTOMATION_RELOADED, context=service_call.context)
 
+    reload_helper = ReloadServiceHelper(reload_service_handler)
+
     async_register_admin_service(
-        hass, DOMAIN, SERVICE_RELOAD, reload_service_handler, schema=vol.Schema({})
+        hass,
+        DOMAIN,
+        SERVICE_RELOAD,
+        reload_helper.execute_service,
+        schema=vol.Schema({}),
     )
 
     return True

homeassistant/helpers/service.py

@@ -783,3 +783,43 @@ def verify_domain_control(
         return check_permissions
 
     return decorator
+
+
+class ReloadServiceHelper:
+    """Helper for reload services to minimize unnecessary reloads."""
+
+    def __init__(self, service_func: Callable[[ServiceCall], Awaitable]):
+        """Initialize ReloadServiceHelper."""
+        self._service_func = service_func
+        self._service_running = False
+        self._service_condition = asyncio.Condition()
+
+    async def execute_service(self, service_call: ServiceCall) -> None:
+        """Execute the service.
+
+        If a previous reload task if currently in progress, wait for it to finish first.
+        Once the previous reload task has finished, one of the waiting tasks will be
+        assigned to execute the reload, the others will wait for the reload to finish.
+        """
+
+        do_reload = False
+        async with self._service_condition:
+            if self._service_running:
+                # A previous reload task is already in progress, wait for it to finish
+                await self._service_condition.wait()
+
+        async with self._service_condition:
+            if not self._service_running:
+                # This task will do the reload
+                self._service_running = True
+                do_reload = True
+            else:
+                # Another task will perform the reload, wait for it to finish
+                await self._service_condition.wait()
+
+        if do_reload:
+            # Reload, then notify other tasks
+            await self._service_func(service_call)
+            async with self._service_condition:
+                self._service_running = False
+                self._service_condition.notify_all()