我正在使用asyncio forever()事件循环。现在，我想在进程或信号或文件更改后重新启动循环（停止循环并重新创建新循环），但是这样做有一些问题：
以下是三个简化的代码段，它们演示了一些协程工作程序和协程循环重启程序：
＃1st尝试：
import asyncio
async def coro_worker(proc):
print(f'Worker: {proc} started.')
while True:
print(f'Worker: {proc} process.')
await asyncio.sleep(proc)
async def reset_loop(loop):
# Some process
for i in range(5): # Like a process.
print(f'{i} counting for reset the eventloop.')
await asyncio.sleep(1)
main(loop) # Expected close the current loop and start a new loop!
def main(previous_loop=None):
offset = 0
if previous_loop is not None: # Trying for close the last loop if exist.
offset = 1 # An offset to change the process name.
for task in asyncio.Task.all_tasks():
print('Cancel the tasks') # Why it increase up?
task.cancel()
# task.clear()
# task.close()
# task.stop()
print("Done cancelling tasks")
asyncio.get_event_loop().stop()
process = [1 + offset, 2 + offset]
loop = asyncio.get_event_loop()
futures = [loop.create_task(coro_worker(proc)) for proc in process]
futures.append(loop.create_task(reset_loop(loop)))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
except asyncio.CancelledError:
print('Tasks has been canceled')
main() # Recursively
finally:
print("Closing Loop")
loop.close()
main()
出[1]：
Worker: 1 started.
Worker: 1 process.
Worker: 2 started.
Worker: 2 process.
0 counting for reset the eventloop.
Worker: 1 process.
1 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
2 counting for reset the eventloop.
Worker: 1 process.
3 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
4 counting for reset the eventloop.
Worker: 1 process.
Cancel the tasks
Cancel the tasks
Cancel the tasks
Done cancelling tasks
Closing Loop
Closing Loop
Task exception was never retrieved
future: <Task cancelling coro=<reset_loop() done, defined at reset_asycio.py:11> exception=RuntimeError('Cannot close a running event loop',)>
Traceback (most recent call last):
File "reset_asycio.py", line 40, in main
loop.run_forever()
File "/usr/lib/python3.6/asyncio/base_events.py", line 425, in run_forever
raise RuntimeError('This event loop is already running')
RuntimeError: This event loop is already running
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "reset_asycio.py", line 17, in reset_loop
main(loop) # Expected close the current loop and start a new loop!
File "reset_asycio.py", line 48, in main
loop.close()
File "/usr/lib/python3.6/asyncio/unix_events.py", line 63, in close
super().close()
File "/usr/lib/python3.6/asyncio/selector_events.py", line 96, in close
raise RuntimeError("Cannot close a running event loop")
RuntimeError: Cannot close a running event loop
Task was destroyed but it is pending!
task: <Task pending coro=<reset_loop() running at reset_asycio.py:11>>
reset_asycio.py:51: RuntimeWarning: coroutine 'reset_loop' was never awaited
main()
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() running at reset_asycio.py:4>>
reset_asycio.py:51: RuntimeWarning: coroutine 'coro_worker' was never awaited
main()
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() running at reset_asycio.py:4>>
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() running at reset_asycio.py:8> wait_for=<Future cancelled>>
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() running at reset_asycio.py:8> wait_for=<Future cancelled>>
＃2尝试：
.
.
.
def main(previous_loop=None):
offset = 0
if previous_loop is not None: # Trying for close the last loop if exist.
previous_loop.stop()
previous_loop.close()
offset = 1 # An offset to change the process name.
process = [1 + offset, 2 + offset]
loop = asyncio.get_event_loop()
futures = [loop.create_task(coro_worker(proc)) for proc in process]
futures.append(loop.create_task(reset_loop(loop)))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
except asyncio.CancelledError:
print('Tasks has been canceled')
main() # Recursively
finally:
print("Closing Loop")
loop.close()
main()
出[2]：
Worker: 1 started.
Worker: 1 process.
Worker: 2 started.
Worker: 2 process.
0 counting for reset the eventloop.
Worker: 1 process.
1 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
2 counting for reset the eventloop.
Worker: 1 process.
3 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
4 counting for reset the eventloop.
Worker: 1 process.
Closing Loop
Task exception was never retrieved
future: <Task finished coro=<reset_loop() done, defined at reset_asycio.py:9> exception=RuntimeError('Cannot close a running event loop',)>
Traceback (most recent call last):
File "reset_asycio.py", line 15, in reset_loop
main(loop) # Expected close the current loop and start new loop!
File "reset_asycio.py", line 21, in main
previous_loop.close()
File "/usr/lib/python3.6/asyncio/unix_events.py", line 63, in close
super().close()
File "/usr/lib/python3.6/asyncio/selector_events.py", line 96, in close
raise RuntimeError("Cannot close a running event loop")
RuntimeError: Cannot close a running event loop
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() done, defined at reset_asycio.py:3> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x7efed846f138>()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<coro_worker() done, defined at reset_asycio.py:3> wait_for=<Future pending cb=[<TaskWakeupMethWrapper object at 0x7efed846f048>()]>>
＃3尝试：
.
.
.
def main(previous_loop=None):
offset = 0
if previous_loop is not None: # Trying for close the last loop if exist.
offset = 1 # An offset to change the process name.
for task in asyncio.Task.all_tasks():
print('Cancel the tasks') # Why it increase up?
task.cancel()
process = [1 + offset, 2 + offset]
loop = asyncio.get_event_loop()
futures = [loop.create_task(coro_worker(proc)) for proc in process]
futures.append(loop.create_task(reset_loop(loop)))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
except asyncio.CancelledError:
print('Tasks has been canceled')
main() # Recursively
finally:
print("Closing Loop")
loop.close()
main()
出[3]：
Worker: 1 started.
Worker: 1 process.
Worker: 2 started.
Worker: 2 process.
0 counting for reset the eventloop.
Worker: 1 process.
1 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
2 counting for reset the eventloop.
Worker: 1 process.
3 counting for reset the eventloop.
Worker: 2 process.
Worker: 1 process.
4 counting for reset the eventloop.
Worker: 1 process.
Cancel the tasks
Cancel the tasks
Cancel the tasks
Closing Loop
Worker: 2 started.
Worker: 2 process.
Worker: 3 started.
Worker: 3 process.
0 counting for reset the eventloop.
1 counting for reset the eventloop.
Worker: 2 process.
2 counting for reset the eventloop.
Worker: 3 process.
3 counting for reset the eventloop.
Worker: 2 process.
4 counting for reset the eventloop.
Cancel the tasks
Cancel the tasks
Cancel the tasks
Cancel the tasks
Cancel the tasks
Cancel the tasks
Closing Loop
Worker: 2 started.
Worker: 2 process.
Worker: 3 started.
Worker: 3 process.
.
.
.
在＃3 try 中，显然我做到了，但是print('Cancel the tasks')在每次重新启动后都会增加，这是什么原因？！
是否有更好的方法来解决此问题？
请原谅我试图简化它的长问题！
[注意]：
asyncio.timeout() 答案 0 :(得分：1)
对main()的递归调用和新的事件循环增加了不必要的复杂性。这是一个更简单的原型可以使用-它监视外部源（文件系统），并且在创建文件时，它只是停止循环。 main()包含一个循环，负责（重新）创建和取消任务：
import os, asyncio, random
async def monitor():
loop = asyncio.get_event_loop()
while True:
if os.path.exists('reset'):
print('reset!')
os.unlink('reset')
loop.stop()
await asyncio.sleep(1)
async def work(workid):
while True:
t = random.random()
print(workid, 'sleeping for', t)
await asyncio.sleep(t)
def main():
loop = asyncio.get_event_loop()
loop.create_task(monitor())
offset = 0
while True:
workers = []
workers.append(loop.create_task(work(offset + 1)))
workers.append(loop.create_task(work(offset + 2)))
workers.append(loop.create_task(work(offset + 3)))
loop.run_forever()
for t in workers:
t.cancel()
offset += 3
if __name__ == '__main__':
main()
另一种选择是永远不要停止事件循环，而只是触发重置事件：
async def monitor(evt):
while True:
if os.path.exists('reset'):
print('reset!')
os.unlink('reset')
evt.set()
await asyncio.sleep(1)
在这种设计中，main()可以是协程：
async def main():
loop = asyncio.get_event_loop()
reset_evt = asyncio.Event()
loop.create_task(monitor(reset_evt))
offset = 0
while True:
workers = []
workers.append(loop.create_task(work(offset + 1)))
workers.append(loop.create_task(work(offset + 2)))
workers.append(loop.create_task(work(offset + 3)))
await reset_evt.wait()
reset_evt.clear()
for t in workers:
t.cancel()
offset += 3
if __name__ == '__main__':
asyncio.run(main())
# or asyncio.get_event_loop().run_until_complete(main())
请注意，在两种变体中，取消任务都是通过await引发CancelledError异常来实现的。该任务一定不能使用try: ... except: ...捕获所有异常，并且如果这样做，则需要重新引发异常。