我在一个项目中使用 asyncio，遇到了这种奇怪的行为。
import asyncio
def schedule_something():
global f
tsk = asyncio.async(do_something())
f = tsk #If this line is commented out, exceptions can be heard.
@asyncio.coroutine
def do_something():
raise Exception()
loop = asyncio.get_event_loop()
loop.call_soon(schedule_something)
loop.run_forever()
loop.close()
出于某种原因，在调用时存储生成的任务会asyncio.async()阻止异常执行任何操作。
有人可以对这种情况有所了解吗？我需要有一种方法来捕获当前项目中的异常。
Task这是因为只有在没有检索到结果的情况下销毁了异常才会引发异常。当您将 分配Task给全局变量时，它将始终具有活动引用，因此永远不会被破坏。在 asyncio/futures.py 中有一个文档字符串对此进行了详细介绍：
class _TracebackLogger:
"""Helper to log a traceback upon destruction if not cleared.
This solves a nasty problem with Futures and Tasks that have an
exception set: if nobody asks for the exception, the exception is
never logged. This violates the Zen of Python: 'Errors should
never pass silently. Unless explicitly silenced.'
However, we don't want to log the exception as soon as
set_exception() is called: if the calling code is written
properly, it will get the exception and handle it properly. But
we *do* want to log it if result() or exception() was never called
-- otherwise developers waste a lot of time wondering why their
buggy code fails silently.
An earlier attempt added a __del__() method to the Future class
itself, but this backfired because the presence of __del__()
prevents garbage collection from breaking cycles. A way out of
this catch-22 is to avoid having a __del__() method on the Future
class itself, but instead to have a reference to a helper object
with a __del__() method that logs the traceback, where we ensure
that the helper object doesn't participate in cycles, and only the
Future has a reference to it.
The helper object is added when set_exception() is called. When
the Future is collected, and the helper is present, the helper
object is also collected, and its __del__() method will log the
traceback. When the Future's result() or exception() method is
called (and a helper object is present), it removes the the helper
object, after calling its clear() method to prevent it from
logging.
如果您想查看/处理异常，只需使用add_done_callback来处理任务的结果，并在遇到异常时执行任何必要的操作：
import asyncio
def handle_result(fut):
if fut.exception():
fut.result() # This will raise the exception.
def schedule_something():
global f
tsk = asyncio.async(do_something())
tsk.add_done_callback(handle_result)
f = tsk
@asyncio.coroutine
def do_something():
raise Exception()
loop = asyncio.get_event_loop()
loop.call_soon(schedule_something)
loop.run_forever()
loop.close()
谢谢，@dano。这是一个自动替换的替代品asyncio.create_task-
def create_task(coro):
task = asyncio.create_task(coro)
return TaskWrapper(task)
class TaskWrapper:
def __init__(self, task):
self.task = task
task.add_done_callback(self.on_task_done)
def __getattr__(self, name):
return getattr(self.task, name)
def __await__(self):
self.task.remove_done_callback(self.on_task_done)
return self.task.__await__()
def on_task_done(self, fut: asyncio.Future):
if fut.cancelled() or not fut.done():
return
fut.result()
def __str__(self):
return f"TaskWrapper<task={self.task}>"
给定示例的更新版本 -
async def do_something():
raise Exception()
async def schedule_something():
global f
tsk = create_task(do_something())
f = tsk # If this line is commented out, exceptions can be heard.
asyncio.run(schedule_something())
$ python test.py
Exception in callback TaskWrapper.on_task_done(<Task finishe...n=Exception()>)
handle: <Handle TaskWrapper.on_task_done(<Task finishe...n=Exception()>)>
Traceback (most recent call last):
File "/Users/dev/.pyenv/versions/3.8.1/lib/python3.8/asyncio/events.py", line 81, in _run
self._context.run(self._callback, *self._args)
File "/Users/dev/Projects/dara/server/bot/async_util.py", line 21, in on_task_done
fut.result()
File "/Users/dev/Projects/dara/server/test.py", line 7, in do_something
raise Exception()
Exception