New submission from Max von Tettenborn:
Below code reproduces the problem. The resulting error is a RecursionError and
it is very hard to trace that to the cause of the problem, which is the runner
task and the stop task yielding from each other, forming a deadlock.
I think, an easy to make mistake like that should raise a clearer exception.
And maybe I am mistaken, but it should in principle be possible for the event
loop to detect a cyclic yield, right?
import asyncio
class A:
@asyncio.coroutine
def start(self):
self.runner_task = asyncio.ensure_future(self.runner())
@asyncio.coroutine
def stop(self):
self.runner_task.cancel()
yield from self.runner_task
@asyncio.coroutine
def runner(self):
try:
while True:
yield from asyncio.sleep(5)
except asyncio.CancelledError:
yield from self.stop()
return
def do_test():
@asyncio.coroutine
def f():
a = A()
yield from a.start()
yield from asyncio.sleep(1)
yield from a.stop()
asyncio.get_event_loop().run_until_complete(f())
--
components: asyncio
messages: 274547
nosy: Max von Tettenborn, gvanrossum, haypo, yselivanov
priority: normal
severity: normal
status: open
title: Confusing error during cyclic yield
type: behavior
versions: Python 3.5
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<http://bugs.python.org/issue27972>
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