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.)

1 files changed, 5 insertions, 2 deletions

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 38c2385..059143f 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -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