我目前在关闭应用程序的CTRL-C期间关闭asyncio协同程序时遇到问题。以下代码是我现在所拥有的精简版本：
#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import asyncio
import time
import functools
import signal
class DummyProtocol(asyncio.Protocol):
def __init__(self, *args, **kwargs):
self._shutdown = asyncio.Event()
self._response = asyncio.Queue(maxsize=1)
super().__init__(*args, **kwargs)
def connection_made(self, transport):
self.transport = transport
def close(self):
print("Closing protocol")
self._shutdown.set()
def data_received(self, data):
#data = b'OK MPD '
# Start listening for commands after a successful handshake
if data.startswith(b'OK MPD '):
print("Ready for sending commands")
self._proxy_task = asyncio.ensure_future(self._send_commands())
return
# saving response for later consumption in self._send_commands
self._response.put_nowait(data)
async def _send_commands(self):
while not self._shutdown.is_set():
print("Waiting for commands coming in ...")
command = None
# listen for commands coming in from the global command queue. Only blocking 1sec.
try:
command = await asyncio.wait_for(cmd_queue.get(), timeout=1)
except asyncio.TimeoutError:
continue
# sending the command over the pipe
self.transport.write(command)
# waiting for the response. Blocking until response is complete.
res = await self._response.get()
# put it into the global response queue
res_queue.put_nowait(res)
async def connect(loop):
c = lambda: DummyProtocol()
t = asyncio.Task(loop.create_connection(c, '192.168.1.143', '6600'))
try:
# Wait for 3 seconds, then raise TimeoutError
trans, proto = await asyncio.wait_for(t, timeout=3)
print("Connected to <192.168.1.143:6600>.")
return proto
except (asyncio.TimeoutError, OSError) as e:
print("Could not connect to <192.168.1.143:6600>. Trying again ...")
if isinstance(e, OSError):
log.exception(e)
def shutdown(proto, loop):
# http://stackoverflow.com/a/30766124/1230358
print("Shutdown of DummyProtocol initialized ...")
proto.close()
# give the coros time to finish
time.sleep(2)
# cancel all other tasks
# for task in asyncio.Task.all_tasks():
# task.cancel()
# stopping the event loop
if loop:
print("Stopping event loop ...")
loop.stop()
print("Shutdown complete ...")
if __name__ == "__main__":
loop = asyncio.get_event_loop()
cmd_queue = asyncio.Queue()
res_queue = asyncio.Queue()
dummy_proto = loop.run_until_complete(connect(loop))
for signame in ('SIGINT','SIGTERM'):
loop.add_signal_handler(getattr(signal, signame), functools.partial(shutdown, dummy_proto, loop))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
finally:
loop.close()
如果按下CTRL-C，会给我以下输出：
Connected to <192.168.1.143:6600>.
Ready for sending commands
Waiting for commands coming in ...
Waiting for commands coming in ...
Waiting for commands coming in ...
Waiting for commands coming in ...
^CShutdown of DummyProtocol initialized ...
Closing protocol
Stopping event loop ...
Shutdown complete ...
Task was destroyed but it is pending!
task: <Task pending coro=<DummyProtocol._send_commands() running at ./dummy.py:45> wait_for=<Future pending cb=[Task._wakeup()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<Queue.get() running at /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/queues.py:168> wait_for=<Future pending cb=[Task._wakeup()]> cb=[_release_waiter(<Future pendi...sk._wakeup()]>)() at /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/tasks.py:344]>
Exception ignored in: <generator object Queue.get at 0x10594b468>
Traceback (most recent call last):
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/queues.py", line 170, in get
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 227, in cancel
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 242, in _schedule_callbacks
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 447, in call_soon
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 456, in _call_soon
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 284, in _check_closed
RuntimeError: Event loop is closed
我对asyncio不太熟悉，所以我很确定我在这里缺少一些重要的东西。令我头疼的是Shutdown complete ...之后输出的一部分。从Task was destroyed but it is pending!开始，我不得不承认我不知道发生了什么。我看了其他问题，但无法让它发挥作用。那么，为什么这段代码输出像Task was destroyed but it is pending! aso.这样的东西以及如何清除协同程序呢？
感谢您的帮助！
答案 0 :(得分：33)
Task was destroyed but it is pending!是什么意思？如果您的程序完成某些asyncio任务仍未完成，那么您将收到此警告。需要此警告，因为正在运行的某些任务可能无法正确释放某些资源。
有两种常见的解决方法：
让我们来看看你的代码：
def shutdown(proto, loop):
print("Shutdown of DummyProtocol initialized ...")
proto.close()
time.sleep(2)
# ...
time.sleep(2) - 此行不会给协程时间完成。它会冻结你的所有程序两秒钟。在此期间什么都不会发生。
这是因为您的事件循环在您调用time.sleep(2)的同一过程中运行。您永远不应该在asyncio程序中以这种方式调用长时间运行的同步操作。请阅读this answer以了解异步代码的工作原理。
让我们尝试修改shutdown函数。这不是异步功能，你不能在其中await内容。要执行一些异步代码，我们需要手动执行：停止当前正在运行的循环（因为它已经在运行），创建一些异步函数来等待已完成的任务，传递此函数以在事件循环中执行。
def shutdown(proto, loop):
print("Shutdown of DummyProtocol initialized ...")
# Set shutdown event:
proto.close()
# Stop loop:
loop.stop()
# Find all running tasks:
pending = asyncio.Task.all_tasks()
# Run loop until tasks done:
loop.run_until_complete(asyncio.gather(*pending))
print("Shutdown complete ...")
您也可以取消任务并等待完成。有关详细信息，请参阅this answer。
我对信号并不熟悉，但是你真的需要赶上CTRL-C吗？每当KeyboardInterrupt发生时，它将按行抛出，在那里运行事件循环（在代码中为loop.run_forever()）。我可能在这里错了，但处理这种情况的常用方法是将所有清理操作放到finally块。
例如，您can see aiohttp如何做到这一点：
try:
loop.run_forever()
except KeyboardInterrupt: # pragma: no branch
pass
finally:
srv.close()
loop.run_until_complete(srv.wait_closed())
loop.run_until_complete(app.shutdown())
loop.run_until_complete(handler.finish_connections(shutdown_timeout))
loop.run_until_complete(app.cleanup())
loop.close()