[3.9] bpo-43406: Fix possible race condition where ``PyErr_CheckSignals`` tries to execute a non-Python signal handler (GH-24756) by miss-islington · Pull Request #24761

[3.9] bpo-43406: Fix possible race condition where ``PyErr_CheckSignals`` tries to execute a non-Python signal handler (GH-24756) by miss-islington · Pull Request #24761 · python/cpython

…ries to execute a non-Python signal handler (pythonGH-24756)

We can receive signals (at the C level, in `trip_signal()` in signalmodule.c) while `signal.signal` is being called to modify the corresponding handler.  Later when `PyErr_CheckSignals()` is called to handle the given signal, the handler may be a non-callable object and would raise a cryptic asynchronous exception.
(cherry picked from commit 68245b7)

Co-authored-by: Antoine Pitrou <antoine@python.org>