New submission from pfreixes:
Having the Event as the way to synchronize 1:N coroutines, the none happy path
should be able to be expressed making possible call the `set_exception` for
each future related to each waiter.
As an example the following code trying to implement a way to avoid the dogpile
effect for a DNS cache. If the coro that holds the event fails, the original
exception is also broadcasted to the waiters.
if key in throttle_dns_events:
yield from throttle_dns_events[key].wait()
else:
throttle_dns_events[key] = Event(loop=loop)
try:
addrs = yield from \
resolver.resolve(host, port, family=family)
cached_hosts.add(key, addrs)
throttle_dns_events[key].set()
except Exception as e:
# any DNS exception, independently of the implementation
# is set for the waiters to raise the same exception.
throttle_dns_events[key].set(exc=e)
raise
finally:
throttle_dns_events.pop(key)
----------
components: asyncio
messages: 294572
nosy: pfreixes, yselivanov
priority: normal
severity: normal
status: open
title: Allow pass an exception to the Event.set method
versions: Python 3.7
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Python tracker <[email protected]>
<http://bugs.python.org/issue30490>
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