[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[William Woodall]

William Woodall  added the comment:

Just an update to my previous post. We ran into this issue again, but only 
noticed later because we do not see this problem on Ubuntu Bionic with Python 
3.6.5, but we did see it again when we tested later on Ubuntu Xenial with 
Python 3.5.1.

See: https://github.com/ros2/launch/issues/84

So this seems to be fixed in later versions, unless it's just hidden now within 
the asyncio debug log messages (though I didn't see anything there either, at a 
glance).

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[山本泰宇]

山本泰宇 added the comment:

> I may workaround the bug during Python finalization if more users report this 
> issue.

+1 in my project:
https://github.com/cybozu/passh/issues/1

Anyway, I'd like to express my gratitude to asyncio.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Chetan Reddy]

Chetan Reddy added the comment:

I'm seeing the same exception as op with Python-3.5.0b4.

I'm writing a function in a library, and am using asyncio to make my function 
run faster. I'd like my library function to be useful even to users who aren't 
using asyncio and therefore won't call get_event_loop().close() at the end of 
their main function.

I can't call get_event_loop().close() in my own library function, because i 
don't want to be closing the event loop in case the user is using the event 
loop.

Is the recommended approach here for me to create my own loop and close it in 
my function (while saving and restoring the existing event loop in case the 
user has already created an event loop)? Guido's comment at 
http://bugs.python.org/msg205027 makes me think not.

The easiest solution might be to not require the user to call 
get_event_loop().close() . This will allow library writers to use 
asyncio.run_until_complete without worrying the user seeing an exception on 
exit. If you agree with this, I'm willing to spend the effort to track down 
this particular exception and provide a patch to fix it.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Chetan Reddy]

Chetan Reddy added the comment:

Disregard my previous comment. I realize now that I shouldn't be calling 
run_until_complete in a library function because it will fail if the user had 
already started running the event loop. I will attempt to use a create and use 
a new event loop in my library function. Apologies for adding noise to this 
page.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[William Woodall]

William Woodall added the comment:

I was getting the same error as the OP in my application.

I did something like this to work around the problem:

import asyncio
import atexit

def close_asyncio_loop():
loop = None
try:
loop = asyncio.get_event_loop()
except AttributeError:
pass
if loop is not None:
loop.close()

atexit.register(close_asyncio_loop)

Is this an appropriate work around?

Why is it up to the application to close the loop explicitly?

Put another way, in what scenario would I want to close the loop outside of the 
application shutting down since it is irreversible?

Thanks in advance for your time.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Joshua Bronson]

Joshua Bronson added the comment:

Quoting Victor Stinner:
  I may workaround the bug during Python finalization if more users report 
 this issue.

Read the above so reporting I'm hitting this too fwiw.

Thanks for the great work on asyncio.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Joshua Bronson]

Joshua Bronson added the comment:

Not sure if it's related / helpful but just in case, since upgrading from 3.4.2 
to 3.4.3, I'm now seeing this printed to stderr sometimes when my program exits:

Exception ignored in: Exception ignored in: Exception ignored in: Exception 
ignored in: Exception ignored in: Exception ignored in: Exception ignored in: 
Exception ignored in: Exception ignored in: Exception ignored in: Exception 
ignored in: Exception ignored in: Exception ignored in: Exception ignored in: 
Exception ignored in: Exception ignored in: Exception ignored in: Exception 
ignored in: Exception ignored in: Exception ignored in: Exception ignored in:

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[STINNER Victor]

STINNER Victor added the comment:

 Exception ignored in: Exception ignored in: ...

Hum, I already saw such issues when exiting an asyncio application. It's 
probably because they are some pending tasks or transports which are never 
closed.

You can try to list tasks at exit using:

loop.close()
print(Task.all_tasks(loop=loop))

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[STINNER Victor]

STINNER Victor added the comment:

I close the issue as wont fix. I may workaround the bug during Python 
finalization if more users report this issue.

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status: open - closed

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Jack O'Connor]

Jack O'Connor added the comment:

Got it, thanks for the heads up.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[STINNER Victor]

STINNER Victor added the comment:

Did you read the latest doc? You should also use the -Wd command line
option to see resource warnings.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[STINNER Victor]

STINNER Victor added the comment:

Debug mode:
https://docs.python.org/dev/library/asyncio-dev.html#asyncio-debug-mode

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Jack O'Connor]

Jack O'Connor added the comment:

@gvanrossum, the last two lines you suggested don't give any error, as 
expected. Not sure why we're getting that error message in the toy example.

@haypo, closing the event loop explicitly works fine for me. But since you 
mentioned it, I don't see any warning when I leave out closing the event loop 
and turn on PYTHONASYNCIODEBUG=1. What should I be seeing?

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[STINNER Victor]

STINNER Victor added the comment:

I'm aware of the issue but I would prefer to not fix it.

The first problem is that you didn't close the event loop. I modified
recently the doc to explain at the begining that you should develop in the
debug mode. In this mode, you will see a warning if you don't close
explicitly the event loop.

The signal issue is that the event loop is closed very late during Python
finalization, and attributes of the signal module are already cleared.

Are you ok to not workaround this specific issue?

Closing an event loop implicitly late can lead to other various bugs.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Guido van Rossum]

Guido van Rossum added the comment:

So this is still strange. When you do this, does it give the same exception?

 import signal
 signal.signal(signal.SIGCHLD, signal.SIG_DFL)

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Jack O'Connor]

Jack O'Connor added the comment:

`close()` fixes it; thanks for the workaround! When I throw a print statement 
inside `remove_signal_handler`, it says that sig is 17 and handler is 0. 17 
looks to be SIGCHLD, presumably from the little echo subprocess exiting in this 
example.

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Jack O'Connor]

New submission from Jack O'Connor:

This toy program:

import asyncio
@asyncio.coroutine
def main():
p = yield from asyncio.create_subprocess_shell('echo hi')
yield from p.wait()
asyncio.get_event_loop().run_until_complete(main())

Produces this output on Arch Linux under Python 3.4.3 (but not 3.4.2):

hi
Exception ignored in: bound method _UnixSelectorEventLoop.__del__ of 
_UnixSelectorEventLoop running=False closed=True debug=False
Traceback (most recent call last):
  File /home/jacko/Downloads/Python-3.4.3/Lib/asyncio/base_events.py, line 
361, in __del__
  File /home/jacko/Downloads/Python-3.4.3/Lib/asyncio/unix_events.py, line 
57, in close
  File /home/jacko/Downloads/Python-3.4.3/Lib/asyncio/unix_events.py, line 
138, in remove_signal_handler
TypeError: signal handler must be signal.SIG_IGN, signal.SIG_DFL, or a callable 
object

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components: asyncio
messages: 236892
nosy: gvanrossum, haypo, oconnor663, yselivanov
priority: normal
severity: normal
status: open
title: TypeError in event loop finalizer, new in Python 3.4.3
type: crash
versions: Python 3.4

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[issue23548] TypeError in event loop finalizer, new in Python 3.4.3

[Guido van Rossum]

Guido van Rossum added the comment:

Does it also have that error if you add `asyncio.get_event_loop().close()` to 
the end of the program?

Can you figure out what the value of `sig` and `handler` are in the traceback?

My gut feeling tells me this is due to `signal.default_int_handler` being None 
at that point in the program tear-down sequence. (Which is why I recommend 
closing the loop.)  The tear-down sequence at best has a partial order, which 
is why this may come and go depending on random variables like which Python 
version you use.

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