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DateTime: use more relaxed ordering constraints #6027

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davidhewitt merged 1 commit into from
May 10, 2026
+4 −4
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DateTime: use more relaxed ordering constraints #6027

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8 changes: 4 additions & 4 deletions pyo3-ffi/src/datetime.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -604,12 +604,12 @@ pub const PyDateTime_CAPSULE_NAME: &CStr = c"datetime.datetime_CAPI";
/// `PyDateTime_IMPORT` is called
#[inline]
pub unsafe fn PyDateTimeAPI() -> *mut PyDateTime_CAPI {
PyDateTimeAPI_impl.load(core::sync::atomic::Ordering::SeqCst)
PyDateTimeAPI_impl.load(Ordering::Acquire)
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@Tpt Tpt May 10, 2026

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we don't need to expose any state here so "acquire" is fine

}

/// Populates the `PyDateTimeAPI` object
pub unsafe fn PyDateTime_IMPORT() {
if PyDateTimeAPI_impl.load(Ordering::SeqCst).is_null() {
if PyDateTimeAPI_impl.load(Ordering::Relaxed).is_null() {
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@Tpt Tpt May 10, 2026

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we just need to check if the value is null, "relaxed" is enough

// PyPy expects the C-API to be initialized via PyDateTime_Import, so trying to use
// `PyCapsule_Import` will behave unexpectedly in pypy.
#[cfg(PyPy)]
Expand All @@ -628,8 +628,8 @@ pub unsafe fn PyDateTime_IMPORT() {
let _ = PyDateTimeAPI_impl.compare_exchange(
ptr::null_mut(),
py_datetime_c_api,
Ordering::SeqCst,
Ordering::SeqCst,
Ordering::Release,
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@Tpt Tpt May 10, 2026

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we don't need to acquire any state here on success (it's done by PyDateTime_IMPORT) so release is enough to expose the state to the other thread.

Similarly on error we don't need to expose anything (no visible change to the other thread) and PyDateTime_IMPORT will acquire the state.

Ordering::Relaxed,
);
}
}
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