CODEWITHSUNDEEP
pythonwindowspython-asynciopython-3.6
jeiea
jeiea

Reputation: 2405

Exception ignored in message on program exit

I initially wanted to do async stream communication on windows. 

from asyncio import *
from asyncio.subprocess import PIPE, STDOUT, DEVNULL
import sys

async def test(exe):
  inst = await create_subprocess_exec(exe, stdin=PIPE, stdout=PIPE, stderr=STDOUT)
  inst.stdin.close()
  inst.wait()

# for subprocess' pipes on Windows
def initialize_async():
  if sys.platform == 'win32':
    set_event_loop(ProactorEventLoop())
  return get_event_loop()

loop = initialize_async()
loop.run_until_complete(test('attrib.exe'))
loop.close()

The above code generates the following.

Exception ignored in: <bound method BaseSubprocessTransport.__del__ of <_WindowsSubprocessTransport closed pid=65088 running stdin=<_ProactorWritePipeTransport closed> stdout=<_ProactorReadPipeTransport closing fd=476 read=<_OverlappedFuture cancelled>>>>
Traceback (most recent call last):
  File "C:\Program Files\Python36\lib\asyncio\base_subprocess.py", line 132, in __del__
    self.close()
  File "C:\Program Files\Python36\lib\asyncio\base_subprocess.py", line 106, in close
    proto.pipe.close()
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 84, in close
    self._loop.call_soon(self._call_connection_lost, None)
  File "C:\Program Files\Python36\lib\asyncio\base_events.py", line 573, in call_soon
    self._check_closed()
  File "C:\Program Files\Python36\lib\asyncio\base_events.py", line 357, in _check_closed
    raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
Exception ignored in: <object repr() failed>
Traceback (most recent call last):
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 95, in __del__
    warnings.warn("unclosed transport %r" % self, ResourceWarning,
  File "C:\Program Files\Python36\lib\asyncio\proactor_events.py", line 54, in __repr__
    info.append('fd=%s' % self._sock.fileno())
  File "C:\Program Files\Python36\lib\asyncio\windows_utils.py", line 152, in fileno
    raise ValueError("I/O operatioon on closed pipe")
ValueError: I/O operatioon on closed pipe

How can I remove this error? stdin.close and wait seems not sufficient.

Upvotes: 3

Views: 2598

Answers (1)

Mikhail Gerasimov
Mikhail Gerasimov

Reputation: 39576

Note, that unlike in synchronous programming many asyncio functions are actually coroutines that should be awaited. See how wait() defined in documentation:

enter image description here

You should fix your code to await this coroutine:

async def test(exe):
  inst = await create_subprocess_exec(exe, stdin=PIPE, stdout=PIPE, stderr=STDOUT)

  data = await inst.stdout.readline()  # readline, for example, is also coroutine.
  print(data)

  await inst.wait()

You won't see any error now.

Upvotes: 1

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