import asyncio import collections from typing import Any, Deque, Optional class EventResultOrError: """Event asyncio lock helper class. Wraps the Event asyncio lock allowing either to awake the locked Tasks without any error or raising an exception. thanks to @vorpalsmith for the simple design. """ def __init__(self, loop: asyncio.AbstractEventLoop) -> None: self._loop = loop self._exc: Optional[BaseException] = None self._event = asyncio.Event() self._waiters: Deque[asyncio.Future[Any]] = collections.deque() def set(self, exc: Optional[BaseException] = None) -> None: self._exc = exc self._event.set() async def wait(self) -> Any: waiter = self._loop.create_task(self._event.wait()) self._waiters.append(waiter) try: val = await waiter finally: self._waiters.remove(waiter) if self._exc is not None: raise self._exc return val def cancel(self) -> None: """Cancel all waiters""" for waiter in self._waiters: waiter.cancel()