_PyOS_SigintEvent() is needed for interruptible waiting on main thread

[jbms]

Bug report

Bug description:

Moved from #108605 (comment)

In #108605, _PyOS_SigintEvent was removed from the public headers.

TensorStore relies on that function here: https://github.com/google/tensorstore/blob/eda046b10158e7d82fdb0f23aeecdfdeb8ac5aa3/python/tensorstore/future.cc#L105 to enable synchronously blocking on the readiness of a custom Future type while allowing Ctrl+C to interrupt when running on the main thread.

The current workaround is to manually declare the function since the symbol is still available.

I'm not aware of a usable alternative. Since signal.set_wakeup_fd only allows a single fd to be set globally, it isn't usable from a library. The best alternative would probably be to poll by waking up every few hundred milliseconds.

CPython versions tested on:

3.13

Operating systems tested on:

No response

[vstinner]

TensorStore relies on that function here: https://github.com/google/tensorstore/blob/eda046b10158e7d82fdb0f23aeecdfdeb8ac5aa3/python/tensorstore/future.cc#L105 to enable synchronously blocking on the readiness of a custom Future type while allowing Ctrl+C to interrupt when running on the main thread.

The problem is that the "sigint event" should not be used in threads other than main. If we add a public function, it should return NULL in this case.

[vstinner]

I found another user of this function by searching for _PyOS_SigintEvent:

billiard-4.2.1.tar.gz: billiard-4.2.1/Modules/_billiard/win32_functions.c: sigint_event = _PyOS_SigintEvent();