问题描述
使用asyncio
时,从信号处理程序回调中抛出自定义异常时遇到问题。
如果我从下面的ShutdownApp
中扔出do_io()
,我就能在run_app()
中正确地抓住它。但是,当从handle_sig()
引发异常时,我似乎无法抓住它。
Minimal,Reproducible Example使用Python 3.8.5测试:
import asyncio
from functools import partial
import os
import signal
from signal import Signals
class ShutdownApp(BaseException):
pass
os.environ["PYTHONASYNCIODEBUG"] = "1"
class App:
def __init__(self):
self.loop = asyncio.get_event_loop()
def _add_signal_handler(self,signal,handler):
self.loop.add_signal_handler(signal,handler,signal)
def setup_signals(self) -> None:
self._add_signal_handler(signal.SIGINT,self.handle_sig)
def handle_sig(self,signum):
print(f"\npid: {os.getpid()},Received signal: {Signals(signum).name},raising error for exit")
raise ShutdownApp("Exiting")
async def do_io(self):
print("io start. Press Ctrl+C Now.")
await asyncio.sleep(5)
print("io end")
def run_app(self):
print("Starting Program")
try:
self.loop.run_until_complete(self.do_io())
except ShutdownApp as e:
print("ShutdownApp caught:",e)
# Todo: do other shutdown related items
except:
print("Other error")
finally:
self.loop.close()
if __name__ == "__main__":
my_app = App()
my_app.setup_signals()
my_app.run_app()
print("Finished")
在异步调试模式下按CTRL+C
(对于SIGINT
)之后的输出:
(env_aiohttp) anav@anav-pc:~/Downloads/test$ python test_asyncio_signal.py
Starting Program
io start. Press Ctrl+C Now.
^C
pid: 20359,Received signal: SIGINT,raising error for exit
Exception in callback App.handle_sig(<Signals.SIGINT: 2>)
handle: <Handle App.handle_sig(<Signals.SIGINT: 2>) created at /home/anav/miniconda3/envs/env_aiohttp/lib/python3.8/asyncio/unix_events.py:99>
source_traceback: Object created at (most recent call last):
File "test_asyncio_signal.py",line 50,in <module>
my_app.setup_signals()
File "test_asyncio_signal.py",line 25,in setup_signals
self._add_signal_handler(signal.SIGINT,self.handle_sig)
File "test_asyncio_signal.py",line 22,in _add_signal_handler
self.loop.add_signal_handler(signal,signal)
File "/home/anav/miniconda3/envs/env_aiohttp/lib/python3.8/asyncio/unix_events.py",line 99,in add_signal_handler
handle = events.Handle(callback,args,self,None)
Traceback (most recent call last):
File "/home/anav/miniconda3/envs/env_aiohttp/lib/python3.8/asyncio/events.py",line 81,in _run
self._context.run(self._callback,*self._args)
File "test_asyncio_signal.py",line 31,in handle_sig
raise ShutdownApp("Exiting")
ShutdownApp: Exiting
io end
Finished
预期输出:
Starting Program
io start. Press Ctrl+C Now.
^C
pid: 20359,raising error for exit
ShutdownApp caught: Exiting
io end
Finished
是否可以从asyncio
中的信号处理程序引发自定义异常?如果是这样,我如何正确捕捉/排除它?
解决方法
handle_sig
是一个回调,因此它直接在事件循环之外运行,并且其异常只是通过全局挂钩报告给用户。如果希望在那里引发的异常在程序的其他地方被捕获,则需要使用将来的方法将异常从handle_sig
转移到您希望其注意到的位置。
要在顶级捕获异常,您可能想引入另一种方法,我们将其称为async_main()
,它等待 self.do_io()
或先前创建的方法将来完成:
def __init__(self):
self.loop = asyncio.get_event_loop()
self.done_future = self.loop.create_future()
async def async_main(self):
# wait for do_io or done_future,whatever happens first
io_task = asyncio.create_task(self.do_io())
await asyncio.wait([self.done_future,io_task],return_when=asyncio.FIRST_COMPLETED)
if self.done_future.done():
io_task.cancel()
await self.done_future # propagate the exception,if raised
else:
self.done_future.cancel()
要从handle_sig
内部引发异常,只需在将来的对象上set the exception:
def handle_sig(self,signum):
print(f"\npid: {os.getpid()},Received signal: {Signals(signum).name},raising error for exit")
self.done_future.set_exception(ShutdownApp("Exiting"))
最后,您对run_app
进行了修改,以将self.async_main()
传递给run_until_complete
,并且一切就绪:
$ python3 x.py
Starting Program
io start. Press Ctrl+C now.
^C
pid: 2069230,Received signal: SIGINT,raising error for exit
ShutdownApp caught: Exiting
Finished
最后,请注意,可靠捕获键盘中断是notoriously tricky undertaking,上面的代码可能无法涵盖所有极端情况。
,如果我从下面的do_io()中抛出ShutdownApp,则可以在run_app()中正确捕获它。但是,当从handle_sig()引发异常时,我似乎无法捕捉到它。
响应以上给出的查询
自定义例外实现:
class RecipeNotValidError(Exception):
def __init__(self):
self.message = "Your recipe is not valid"
try:
raise RecipeNotValidError
except RecipeNotValidError as e:
print(e.message)
在handle_sig方法中,添加try和except块。另外,您可以在自定义例外中自定义消息。
def handle_sig(self,signum):
try:
print(f"\npid: {os.getpid()},raising
error for exit")
raise ShutdownApp("Exiting")
except ShutdownApp as e:
print(e.message)
针对您的第二个查询: 是否可以从asyncio中的信号处理程序引发自定义异常?如果是这样,我如何正确捕捉/排除它?
Asyncio中的内置错误处理。有关更多文档,请访问https://docs.python.org/3/library/asyncio-exceptions.html
import asyncio
async def f():
try:
while True: await asyncio.sleep(0)
except asyncio.CancelledError:
print('I was cancelled!')
else:
return 111