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bpo-39622: Interrupt the main asyncio task on Ctrl+C (GH-32105)

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Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
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Andrew Svetlov 2022-03-30 15:15:06 +03:00 • committed by GitHub
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27
Doc/library/asyncio-runner.rst
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@ -119,3 +119,30 @@ Runner context manager
Embedded *loop* and *context* are created at the :keyword:`with` body entering
or the first call of :meth:`run` or :meth:`get_loop`.
Handling Keyboard Interruption
==============================
.. versionadded:: 3.11
When :const:`signal.SIGINT` is raised by :kbd:`Ctrl-C`, :exc:`KeyboardInterrupt`
exception is raised in the main thread by default. However this doesn't work with
:mod:`asyncio` because it can interrupt asyncio internals and can hang the program from
exiting.
To mitigate this issue, :mod:`asyncio` handles :const:`signal.SIGINT` as follows:
1. :meth:`asyncio.Runner.run` installs a custom :const:`signal.SIGINT` handler before
any user code is executed and removes it when exiting from the function.
2. The :class:`~asyncio.Runner` creates the main task for the passed coroutine for its
execution.
3. When :const:`signal.SIGINT` is raised by :kbd:`Ctrl-C`, the custom signal handler
cancels the main task by calling :meth:`asyncio.Task.cancel` which raises
:exc:`asyncio.CancelledError` inside the the main task. This causes the Python stack
to unwind, ``try/except`` and ``try/finally`` blocks can be used for resource
cleanup. After the main task is cancelled, :meth:`asyncio.Runner.run` raises
:exc:`KeyboardInterrupt`.
4. A user could write a tight loop which cannot be interrupted by
:meth:`asyncio.Task.cancel`, in which case the second following :kbd:`Ctrl-C`
immediately raises the :exc:`KeyboardInterrupt` without cancelling the main task.