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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()