大家晚上好，我正在尝试创建互联网机器人，我在将我的脚本从python 3.4迁移到3.5或3.6+时遇到了问题。它使用asyncio并且在3.4 python上运行良好但是当我用python3.5 +启动它时出现错误：RuntimeError: Cannot run the event loop while another loop is running
这是代码方案：
import multiprocessing as mp
import asyncio
import concurrent.futures
import aiohttp
def create_proccesses(separate_loop_creator, coro):
proccesses = []
for n in range(2):
proc = mp.Process(target=separate_loop_creator, args=(coro,))
proc.start()
proccesses.append(proc)
for p in proccesses:
p.join()
def separate_loop_creator(coro):
sep_loop = asyncio.new_event_loop()
asyncio.set_event_loop(sep_loop)
tasks = [asyncio.async(coro(sep_loop)) for _ in range(100)]
try:
sep_loop.run_until_complete(asyncio.wait(tasks))
sep_loop.close()
except Exception as err:
print(err)
for task in tasks:
task.cancel()
sep_loop.close()
@asyncio.coroutine
def manager(exe, loop):
# some calculations and start coros in several processes
loop.run_in_executor(
exe,
create_proccesses,
separate_loop_creator,
some_coro
)
@asyncio.coroutine
def some_work_in_mainloop():
while True:
print('Some server dealing with connections here...')
yield from asyncio.sleep(1)
@asyncio.coroutine
def some_coro(loop):
with aiohttp.ClientSession(loop=loop) as session:
response = yield from session.get('http://google.com')
yield from asyncio.sleep(2)
print(response.status)
if __name__ == '__main__':
mainloop = asyncio.get_event_loop()
executor = concurrent.futures.ProcessPoolExecutor(5)
asyncio.async(some_work_in_mainloop())
asyncio.async(manager(executor, mainloop))
try:
mainloop.run_forever()
finally:
mainloop.close()
separate_loop_creator()协程中的异常提升，它是RuntimeError: Cannot run the event loop while another loop is running。我认为这是因为改变了get_event_loop()机制，但我不明白我的代码有什么问题。
这是我想要做的：
+--------------+
+-------+other service |
+----------+ +--------------+
| mainloop |
+----------+
| +------------+
+-----+ executor |
+------+-----+
|
+------+--------+
|start proccess |
+---+-------+---+
+-----------------+ | | +---------------+
|start new loop +------+ +------+ start new loop|
+--------+--------+ +-------+-------+
| |
+-------+-------+ +------v-------+
| run coro | | run coro |
+---------------+ +--------------+
这是我在python3.5.3上获得的痕迹：
Traceback (most recent call last):
File "tst.py", line 21, in separate_loop_creator
sep_loop.run_until_complete(asyncio.wait(tasks))
File "/root/.pyenv/versions/3.5.3/lib/python3.5/asyncio/base_events.py", line 454, in run_until_complete
self.run_forever()
File "/root/.pyenv/versions/3.5.3/lib/python3.5/asyncio/base_events.py", line 411, in run_forever
'Cannot run the event loop while another loop is running')
RuntimeError: Cannot run the event loop while another loop is running
Cannot run the event loop while another loop is running
Traceback (most recent call last):
File "tst.py", line 21, in separate_loop_creator
sep_loop.run_until_complete(asyncio.wait(tasks))
File "/root/.pyenv/versions/3.5.3/lib/python3.5/asyncio/base_events.py", line 454, in run_until_complete
self.run_forever()
File "/root/.pyenv/versions/3.5.3/lib/python3.5/asyncio/base_events.py", line 411, in run_forever
'Cannot run the event loop while another loop is running')
RuntimeError: Cannot run the event loop while another loop is running
Python 3.4.3结果：
...
200
Some server dealing with connections here...
200
200
Some server dealing with connections here...
200
200
Some server dealing with connections here...
200
...
答案 0 :(得分：6)
这实际上是CPython 3.6.0中asyncio的一个错误。有一个PR来解决这个问题，因此3.6.1按预期工作。
作为一种解决方法，您可以在项目中添加以下代码：
import sys
if sys.version_info[:3] == (3, 6, 0):
import asyncio.events as _ae
import os as _os
_ae._RunningLoop._pid = None
def _get_running_loop():
if _ae._running_loop._pid == _os.getpid():
return _ae._running_loop._loop
def _set_running_loop(loop):
_ae._running_loop._pid = _os.getpid()
_ae._running_loop._loop = loop
_ae._get_running_loop = _get_running_loop
_ae._set_running_loop = _set_running_loop
答案 1 :(得分：1)
最好的解决方案，如果可能的话，尝试从程序中完全删除multiprocessing，并且只使用一个事件循环（可选择使用ProcessPoolExecutor进行隔离的CPU密集型任务）。
截至2017-03-02，此问题存在一个开放的python错误，影响非Windows平台：https://bugs.python.org/issue22087。
这是一个触发相同问题的较短程序：
import asyncio
import multiprocessing as mp
def create_another_loop():
loop = asyncio.new_event_loop()
loop.run_forever()
async def create_process():
proc = mp.Process(target=create_another_loop)
proc.start()
proc.join()
if __name__ == '__main__':
main_loop = asyncio.get_event_loop()
main_loop.run_until_complete(create_process())
main_loop.close()
一个hackish解决方法（小心！使用后果自负！）受到此处https://github.com/python/asyncio/pull/497建议修复的启发，将此代码添加到新创建的Process：
if asyncio.events._running_loop:
asyncio.events._running_loop._loop = None
示例：
import asyncio
import multiprocessing as mp
import time
from concurrent.futures.process import ProcessPoolExecutor
async def clock(label, n=5, sleep=1):
print(label, "start")
for i in range(n):
await asyncio.sleep(sleep)
print(label, i + 1)
print(label, "end")
return label
def create_another_loop():
# HACK START
if asyncio.events._running_loop:
asyncio.events._running_loop._loop = None
# HACK END
loop = asyncio.new_event_loop()
loop.run_until_complete(clock("sub"))
loop.close()
def create_process():
time.sleep(2)
proc = mp.Process(target=create_another_loop)
proc.start()
proc.join()
return "ok"
async def create_process_in_pool():
return await main_loop.run_in_executor(ProcessPoolExecutor(), create_process)
if __name__ == '__main__':
main_loop = asyncio.get_event_loop()
tasks = (
clock("main"),
create_process_in_pool(),
)
print(main_loop.run_until_complete(asyncio.gather(*tasks)))
main_loop.close()
其他可能的解决方法：在开始循环之前创建流程或使用甚至允许asyncio.create_subprocess_exec的communicate with the subprocess via a stream。