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bpo-46771: Remove two controversial lines from Task.cancel() (GH-31623)
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.)
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@ -205,8 +205,11 @@ def cancel(self, msg=None):
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if self.done():
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return False
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self._num_cancels_requested += 1
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if self._num_cancels_requested > 1:
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return False
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# These two lines are controversial. See discussion starting at
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# https://github.com/python/cpython/pull/31394#issuecomment-1053545331
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# Also remember that this is duplicated in _asynciomodule.c.
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# if self._num_cancels_requested > 1:
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# return False
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if self._fut_waiter is not None:
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if self._fut_waiter.cancel(msg=msg):
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# Leave self._fut_waiter; it may be a Task that
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@ -514,7 +514,11 @@ async def task():
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self.assertTrue(t.cancel())
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self.assertTrue(t.cancelling())
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self.assertIn(" cancelling ", repr(t))
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self.assertFalse(t.cancel())
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# Since we commented out two lines from Task.cancel(),
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# this t.cancel() call now returns True.
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# self.assertFalse(t.cancel())
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self.assertTrue(t.cancel())
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with self.assertRaises(asyncio.CancelledError):
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loop.run_until_complete(t)
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@ -2206,9 +2206,13 @@ _asyncio_Task_cancel_impl(TaskObj *self, PyObject *msg)
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}
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self->task_num_cancels_requested += 1;
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if (self->task_num_cancels_requested > 1) {
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Py_RETURN_FALSE;
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}
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// These three lines are controversial. See discussion starting at
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// https://github.com/python/cpython/pull/31394#issuecomment-1053545331
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// and corresponding code in tasks.py.
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// if (self->task_num_cancels_requested > 1) {
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// Py_RETURN_FALSE;
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// }
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if (self->task_fut_waiter) {
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PyObject *res;
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