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bpo-46771: Remove two controversial lines from Task.cancel() (GH-31623)

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Also from the _asyncio C accelerator module,
and adjust one test that the change caused to fail.

For more discussion see the discussion starting here:
https://github.com/python/cpython/pull/31394#issuecomment-1053545331

(Basically, @asvetlov proposed to return False from cancel()
when there is already a pending cancellation, and I went along,
even though it wasn't necessary for the task group implementation,
and @agronholm has come up with a counterexample that fails
because of this change.  So now I'm changing it back to the old
semantics (but still bumping the counter) until we can have a
proper discussion about this.)
This commit is contained in:
Guido van Rossum 2022-02-28 15:15:56 -08:00 • committed by GitHub
parent 08deed1af5
commit 7d611b4cab
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3 changed files with 17 additions and 6 deletions
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7
Lib/asyncio/tasks.py
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@ -205,8 +205,11 @@ class Task(futures._PyFuture): # Inherit Python Task implementation
if self.done():
return False
self._num_cancels_requested += 1
if self._num_cancels_requested > 1:
return False
# These two lines are controversial. See discussion starting at
# https://github.com/python/cpython/pull/31394#issuecomment-1053545331
# Also remember that this is duplicated in _asynciomodule.c.
# if self._num_cancels_requested > 1:
# return False
if self._fut_waiter is not None:
if self._fut_waiter.cancel(msg=msg):
# Leave self._fut_waiter; it may be a Task that