[issue26520] asyncio.new_event_loop() hangs

[Erwin Mayer]

New submission from Erwin Mayer:

I am using the following function to force a coroutine to run synchronously:

def await_sync(coro: types.CoroutineType, timeout_s: int=None):
    """

    :param coro: a coroutine or lambda loop: coroutine(loop)
    :param timeout_s:
    :return:
    """
    loop = asyncio.new_event_loop()  # type: BaseEventLoop
    if not is_awaitable(coro):
        coro = coro(loop)
    if timeout_s is None:
        fut = asyncio.ensure_future(coro, loop=loop)
    else:
        fut = asyncio.ensure_future(asyncio.wait_for(coro, timeout=timeout_s, loop=loop), loop=loop)
    loop.run_until_complete(fut)
    return fut.result()

def is_awaitable(coro_or_future):
    if isinstance(coro_or_future, futures.Future):
        return coro_or_future
    elif asyncio.coroutines.iscoroutine(coro_or_future):
        return True
    elif asyncio.compat.PY35 and inspect.isawaitable(coro_or_future):
        return True
    else:
        return False

However, intermittently, it will freeze upon simply trying to create a new loop: loop = asyncio.new_event_loop(). Inspecting the stack traces shows me the exact location where it hangs:

File: "/src\system\utils.py", line 34, in await_sync
  loop = asyncio.new_event_loop()  # type: BaseEventLoop
File: "\lib\asyncio\events.py", line 636, in new_event_loop
  return get_event_loop_policy().new_event_loop()
File: "\lib\asyncio\events.py", line 587, in new_event_loop
  return self._loop_factory()
File: "\lib\asyncio\selector_events.py", line 55, in __init__
  self._make_self_pipe()
File: "\lib\asyncio\selector_events.py", line 116, in _make_self_pipe
  self._ssock, self._csock = self._socketpair()
File: "\lib\asyncio\windows_events.py", line 295, in _socketpair
  return windows_utils.socketpair()
File: "\lib\socket.py", line 515, in socketpair
  ssock, _ = lsock.accept()
File: "\lib\socket.py", line 195, in accept
  fd, addr = self._accept()

I am using Python 3.5.1.

StackOverflow question: http://stackoverflow.com/questions/35861175/what-can-cause-asyncio-to-hang-upon-simply-creating-a-new-loop

----------
components: asyncio
messages: 261440
nosy: Erwin Mayer, gvanrossum, haypo, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.new_event_loop() hangs
type: crash
versions: Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue26520>
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