Importing python module causes SIGINT to be ignored

[MarkTuddenham]

Bug Description

Importing some python modules from rust causes a SIGINT signal to be ignored, even after python is no longer in scope.

(I'm not sure if the problem is PyO3, tokio, or if I haven't used the interface properly, so please let me know if this is the wrong place for this issue.)

Steps to Reproduce

cargo run can be interrupted with CTRL-C, but cargo run -F hang cannot.

---

main.rs

use std::time::Duration;

use pyo3::prelude::*;

#[tokio::main(flavor = "current_thread")]
async fn main() {
    #[cfg(feature = "hang")]
    run("foo");

    #[cfg(not(feature = "hang"))]
    run("bar");

    println!("Finished with pyo3");

    let handle = tokio::spawn(async {
        tokio::time::sleep(Duration::from_millis(10_000)).await
    });
    handle.await.unwrap();
}

pub fn run(name: &str) {
    let src_str = "
def foo():
    import matplotlib

def bar():
    import os
    ";
    Python::with_gil(|py| {
        let module: &PyModule = PyModule::from_code(py, src_str, "", "").unwrap();
        let _res = module.getattr(name).unwrap().call0();
    });
}

Cargo.toml

[package]
name = "pyo3_test"
version = "0.1.0"
edition = "2021"

[features]
hang = []

[dependencies]
tokio = { version = "1.20.1", features = ["macros", "rt", "time"] }
pyo3 = { version = "0.16.5", features = ["auto-initialize"]}

Backtrace

No response

Your operating system and version

Ubuntu 20.04.4 / Linux 5.4.0-124-generic

Your Python version (python --version)

Python 3.8.5

Your Rust version (rustc --version)

rustc 1.63.0 (4b91a6ea7 2022-08-08)

Your PyO3 version

0.16.5

How did you install python? Did you use a virtualenv?

miniconda Occurs both with and without virualenv.

Additional Info

No response

[davidhewitt]

I can reproduce this, also tried 3.10 and 3.11rc1 with the same result. matplotlib isn't necessary for the repro, the offending module is the builtin _signal module (which matplotlib imports).

For background, PyO3 calls Py_InitializeEx(0) which instructs Python not to install signal handlers, but it looks like if the _signal module is imported then Python installs signal handlers anyway. I don't know whether this is by design, or a bug, but it definitely seems like there's not much we can do about it without upstream help.