Raise error if EventEmitter used with async callback

Author: bcherry

examples/participant_attributes.py

@@ -24,7 +24,7 @@ async def main(room: rtc.Room) -> None:
     )
 
     @room.on("participant_attributes_changed")
-    def on_participant_attributes_changed(
+    async def on_participant_attributes_changed(
         changed_attributes: dict[str, str], participant: rtc.Participant
     ):
         logging.info(

livekit-rtc/livekit/rtc/event_emitter.py

@@ -1,4 +1,5 @@
 import inspect
+import asyncio
 from typing import Callable, Dict, Set, Optional, Generic, TypeVar
 
 from .log import logger
@@ -156,6 +157,11 @@ def greet(name):
             ```
         """
         if callback is not None:
+            if asyncio.iscoroutinefunction(callback):
+                raise ValueError(
+                    "Cannot register an async callback with `.on()`. Use `asyncio.create_task` within your synchronous callback instead."
+                )
+
             if event not in self._events:
                 self._events[event] = set()
             self._events[event].add(callback)