Subinterpreters running on the main thread should handle signals

Feature or enhancement

Proposal:

It's currently impossible to interrupt long-running operations inside subinterpreters:

from concurrent import interpreters

interp = interpreters.create()
interp.exec("import time; time.sleep(100)")  # Cannot CTRL^C!

This is because _Py_ThreadCanHandleSignals explicitly requires the main interpreter:

https://github.com/python/cpython/blob/7040aa54f14676938970e10c5f74ea93cd56aa38/Include/internal/pycore_pystate.h#L82-L86

After thinking about this for a while, I can't see any real reason why stdlib interpreters shouldn't be able to handle signals (in the main thread). It's probably a slight compatibility break for legacy C API subinterpreters, so we can just disable it for them (and add the new option to handle signals behind an interpreter configuration setting).

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

Quickly discussed in-person a few months ago with @ericsnowcurrently and @colesbury. I don't think we came to a consensus, but there wasn't any pushback as far as I could tell.

Linked PRs

• gh-137174

Leia Include/internal/pycore_pystate.h em _Py_ThreadCanHandleSignals e o exemplo de concurrent.interpreters na issue. Revise o PR vinculado gh-137174 antes de prosseguir; isso permitiria que Ctrl-C interrompesse operações de longa duração em subinterpretadores da thread principal, preservando a compatibilidade com a C API legada indicada.