Expose unsafe wrappers for Py_BEGIN_CRITICAL_SECTION_MUTEX API #5642
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davidhewitt
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Nov 21, 2025
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ngoldbaum
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Nov 24, 2025
| /// while the closure `f` is executing. The critical section may be temporarily | ||
| /// released and re-acquired if the closure calls back into the interpreter in | ||
| /// a manner that would block. This is similar to how the GIL can be released | ||
| /// during blocking calls. See the safety notes below for caveats about |
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ngoldbaum
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Nov 24, 2025
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I marked this ready for review but I expect it to have at least one more round. I left a couple questions for others and comments for myself inline. |
davidhewitt
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src/sync.rs
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| #[cfg_attr(not(Py_GIL_DISABLED), allow(unused_variables))] | ||
| pub fn with_critical_section_mutex<'py, F, R, T>(_py: Python<'py>, mutex: &PyMutex<T>, f: F) -> R | ||
| where | ||
| F: FnOnce(&UnsafeCell<T>) -> R, |
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One way to make the "safety" of this clearer would be to package the UnsafeCell up as something like
struct EnteredCriticalSection<'a, T>(&'a UnsafeCell<T>);
impl<T> EnteredCriticalSection<'_, T> {
unsafe fn get(&mut self) -> &mut T { ... }
}Can then document safety invariants on the get function. It's also a bit nicer than users having to go through UnsafeCell::get themselves (and a raw pointer).
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Done, see latest changes.
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Python 3.14 introduced new variants for the critical section macros that accept a PyMutex instead of a PyObject. See python/cpython#133296, capi-workgroup/decisions#67, and python/cpython#135899 for more details.
I also was responsible for making sure this landed in 3.14, so shipping this PR is special to me as it completes the loop :)
So far I don't think there are any open source uses yet because it's so new and it's 3.14-specific.
The new APIs accept an
EnteredCriticalSectionwhich exposes unsafegetandget_mutmethods because the caller needs to guarantee that the closure doesn't unsafely release the resource protected by the PyMutex.I also expanded the docs for the existing critical section API wrappers to clarify things a bit.