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PyO3
Segmentation fault possibly related to thread locals
Bug Description
We're using PyO3 for Zensical and get a segmentation fault which seems to be related to the cleanup of thread locals. Specifically, calling torch.set_default_device("cpu") triggers the issue. We're calling Python from a worker thread. When moving the call to the main thread, the segfault disappears.
This is the core of this minimal reproduction (repo):
py.detach(|| {
thread::spawn(|| {
Python::attach(|py| {
let code = CString::new(r"
import torch
print('Hello from Python')
torch.set_default_device('cpu')
").unwrap();
py.run(&code, None, None).expect("Failed to run Python code");
});
}).join().expect("Thread panicked");
});
When removing wrapping with thread:spawn, the problem disappears.
Steps to Reproduce
git clone [email protected]:squidfunk/zensical-issue-71.git
cd zensical-issue-71
uv venv
. ./.venv/bin/activate
uv sync
uv run maturin develop
python python/demo/main.py
Backtrace
Your operating system and version
macOS 13.7
Your Python version (python --version)
3.13.6
Your Rust version (rustc --version)
rustc 1.93.0
Your PyO3 version
0.27.1
How did you install python? Did you use a virtualenv?
uv + virtualenv
Additional Info
Likely related:
- https://github.com/PyO3/pyo3/issues/5359
- https://github.com/PyO3/pyo3/issues/2611
- https://github.com/zensical/zensical/issues/71
