Andrew Svetlov <[email protected]> added the comment:
I have no good simple real-case scenario, sorry.
There is a demonstration of my thoughts.
Suppose we have a custom context manager that behaves similar to timeout() but
is controlled not by timer but external event source (it could be an
invalidation message sent by a distributed broker or something else).
class EventRaised(Exception):
pass
class CancelOnEvent:
async def __init__(self, event):
self.event = event
async def __aenter__(self):
self.waiter = asyncio.task(self._cancel_on_event,
asyncio.current_task())
async def __aexit__(self, exc_typ, ecx_val, exc_tb):
if exc_typ is asyncio.CancelledError:
if CASE1: # <<< cleanup strategy selector
if asyncio.current_task().uncancel() == 0:
raise EventRaised
else:
if self.event.is_set():
raise EventRaised
async def _cancel_on_event(self, task):
await self.event.wait()
task.cancel()
###########
event = asyncio.Event()
async with asyncio.timeout(1): # what exception should bubble-up here?
async with CancelOnEvent(event):
await asyncio.sleep(10) # event.set() is called here after 1 sec
timeout
If this CancelOnEvent context manager is used together with timeout() CM, is
the behavior clear? Should `.uncancel()` be used by CancelOnEvent? Why? How
should it interact with timeout()?
I have no clear and obvious answer on these questions, this worries me.
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<https://bugs.python.org/issue46771>
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