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bpo-31033: Add a msg argument to Future.cancel() and Task.cancel() (GH-19979)

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Chris Jerdonek 2020-05-15 16:55:50 -07:00 • committed by GitHub
parent fe1176e882
commit 1ce5841eca
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10 changed files with 355 additions and 70 deletions
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11
Lib/asyncio/futures.py
View file

@ -51,6 +51,7 @@ class Future:
_exception = None
_loop = None
_source_traceback = None
_cancel_message = None
# This field is used for a dual purpose:
# - Its presence is a marker to declare that a class implements
@ -123,7 +124,7 @@ class Future:
raise RuntimeError("Future object is not initialized.")
return loop
def cancel(self):
def cancel(self, msg=None):
"""Cancel the future and schedule callbacks.
If the future is already done or cancelled, return False. Otherwise,
@ -134,6 +135,7 @@ class Future:
if self._state != _PENDING:
return False
self._state = _CANCELLED
self._cancel_message = msg
self.__schedule_callbacks()
return True
@ -173,7 +175,9 @@ class Future:
the future is done and has an exception set, this exception is raised.
"""
if self._state == _CANCELLED:
raise exceptions.CancelledError
raise exceptions.CancelledError(
'' if self._cancel_message is None else self._cancel_message)
if self._state != _FINISHED:
raise exceptions.InvalidStateError('Result is not ready.')
self.__log_traceback = False
@ -190,7 +194,8 @@ class Future:
InvalidStateError.
"""
if self._state == _CANCELLED:
raise exceptions.CancelledError
raise exceptions.CancelledError(
'' if self._cancel_message is None else self._cancel_message)
if self._state != _FINISHED:
raise exceptions.InvalidStateError('Exception is not set.')
self.__log_traceback = False

36
Lib/asyncio/tasks.py
View file

@ -230,7 +230,7 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
"""
return base_tasks._task_print_stack(self, limit, file)
def cancel(self):
def cancel(self, msg=None):
"""Request that this task cancel itself.
This arranges for a CancelledError to be thrown into the
@ -254,13 +254,14 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
if self.done():
return False
if self._fut_waiter is not None:
if self._fut_waiter.cancel():
if self._fut_waiter.cancel(msg=msg):
# Leave self._fut_waiter; it may be a Task that
# catches and ignores the cancellation so we may have
# to cancel it again later.
return True
# It must be the case that self.__step is already scheduled.
self._must_cancel = True
self._cancel_message = msg
return True
def __step(self, exc=None):
@ -269,7 +270,8 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
f'_step(): already done: {self!r}, {exc!r}')
if self._must_cancel:
if not isinstance(exc, exceptions.CancelledError):
exc = exceptions.CancelledError()
exc = exceptions.CancelledError(''
if self._cancel_message is None else self._cancel_message)
self._must_cancel = False
coro = self._coro
self._fut_waiter = None
@ -287,11 +289,15 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
if self._must_cancel:
# Task is cancelled right before coro stops.
self._must_cancel = False
super().cancel()
super().cancel(msg=self._cancel_message)
else:
super().set_result(exc.value)
except exceptions.CancelledError:
super().cancel() # I.e., Future.cancel(self).
except exceptions.CancelledError as exc:
if exc.args:
cancel_msg = exc.args[0]
else:
cancel_msg = None
super().cancel(msg=cancel_msg) # I.e., Future.cancel(self).
except (KeyboardInterrupt, SystemExit) as exc:
super().set_exception(exc)
raise
@ -319,7 +325,8 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
self.__wakeup, context=self._context)
self._fut_waiter = result
if self._must_cancel:
if self._fut_waiter.cancel():
if self._fut_waiter.cancel(
msg=self._cancel_message):
self._must_cancel = False
else:
new_exc = RuntimeError(
@ -716,12 +723,12 @@ class _GatheringFuture(futures.Future):
self._children = children
self._cancel_requested = False
def cancel(self):
def cancel(self, msg=None):
if self.done():
return False
ret = False
for child in self._children:
if child.cancel():
if child.cancel(msg=msg):
ret = True
if ret:
# If any child tasks were actually cancelled, we should
@ -780,7 +787,8 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
# Check if 'fut' is cancelled first, as
# 'fut.exception()' will *raise* a CancelledError
# instead of returning it.
exc = exceptions.CancelledError()
exc = exceptions.CancelledError(''
if fut._cancel_message is None else fut._cancel_message)
outer.set_exception(exc)
return
else:
@ -799,7 +807,9 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
# Check if 'fut' is cancelled first, as
# 'fut.exception()' will *raise* a CancelledError
# instead of returning it.
res = exceptions.CancelledError()
res = exceptions.CancelledError(
'' if fut._cancel_message is None else
fut._cancel_message)
else:
res = fut.exception()
if res is None:
@ -810,7 +820,9 @@ def gather(*coros_or_futures, loop=None, return_exceptions=False):
# If gather is being cancelled we must propagate the
# cancellation regardless of *return_exceptions* argument.
# See issue 32684.
outer.set_exception(exceptions.CancelledError())
exc = exceptions.CancelledError(''
if fut._cancel_message is None else fut._cancel_message)
outer.set_exception(exc)
else:
outer.set_result(results)

8
Lib/asyncio/windows_events.py
View file

@ -75,9 +75,9 @@ class _OverlappedFuture(futures.Future):
self._loop.call_exception_handler(context)
self._ov = None
def cancel(self):
def cancel(self, msg=None):
self._cancel_overlapped()
return super().cancel()
return super().cancel(msg=msg)
def set_exception(self, exception):
super().set_exception(exception)
@ -149,9 +149,9 @@ class _BaseWaitHandleFuture(futures.Future):
self._unregister_wait_cb(None)
def cancel(self):
def cancel(self, msg=None):
self._unregister_wait()
return super().cancel()
return super().cancel(msg=msg)
def set_exception(self, exception):
self._unregister_wait()