import asyncio

import collections

class EventResultOrError:

"""

This class wrappers the Event asyncio lock allowing either awake the

locked Tasks without any error or raising an exception.

thanks to @vorpalsmith for the simple design.

"""

def __init__(self, loop):

self._loop = loop

self._exc = None

self._event = asyncio.Event(loop=loop)

self._waiters = collections.deque()

def set(self, exc=None):

self._exc = exc

self._event.set()

async def wait(self):

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):

""" Cancel all waiters """

for waiter in self._waiters:

waiter.cancel()