Hi all
Below is a simple asyncio loop that runs two background tasks.
They both perform a simple count. The first one counts forever, wrapped in a
try/except. The second one counts up to 5, then cancels the first one and
stops the loop.
There are two ways of ensuring that then cancellation is complete -
asyncio.wait([a sequence of futures])
asyncio.wait_for(a single future)
Both take an optional timeout.
If I use the first method without a timeout, the cancellation completes and
the loop stops.
If I use the second method without a timeout, the future is cancelled, but
the program hangs.
If I add a timeout to the second one, it behaves the same as the first one.
Is there a reason for this?
I am using version 3.6.0.
Thanks
Frank Millman
import asyncio
from itertools import count
async def counter1():
cnt = count(1)
try:
while True:
print('From 1:', next(cnt))
await asyncio.sleep(1)
except asyncio.CancelledError:
print('counter1 cancelled')
async def counter2():
cnt = count(1)
for i in range(5):
print('From 2:', next(cnt))
await asyncio.sleep(1)
cnt1.cancel()
# await asyncio.wait([cnt1]) # works
# await asyncio.wait_for(cnt1) # hangs
await asyncio.wait_for(cnt1, 1) # works
loop.stop()
loop = asyncio.get_event_loop()
cnt1 = asyncio.ensure_future(counter1())
cnt2 = asyncio.ensure_future(counter2())
loop.run_forever()
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