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convert module initialization to use pep 489 slots #4081

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convert module initialization to use pep 489 slots #4081

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4 changes: 2 additions & 2 deletions pyo3-macros-backend/src/module.rs
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Expand Up @@ -369,8 +369,8 @@ fn module_initialization(options: PyModuleOptions, ident: &syn::Ident) -> TokenS
/// the module.
#[doc(hidden)]
#[export_name = #pyinit_symbol]
pub unsafe extern "C" fn __pyo3_init() -> *mut #pyo3_path::ffi::PyObject {
#pyo3_path::impl_::trampoline::module_init(|py| _PYO3_DEF.make_module(py))
pub unsafe extern "C" fn __pyo3_init() -> *mut #pyo3_path::ffi::PyModuleDef {
_PYO3_DEF.make_def()
}
}
}
Expand Down
40 changes: 31 additions & 9 deletions src/impl_/pymodule.rs
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Expand Up @@ -2,6 +2,7 @@

use std::{cell::UnsafeCell, marker::PhantomData};

use parking_lot::Once;
#[cfg(all(
not(any(PyPy, GraalPy)),
Py_3_9,
Expand All @@ -19,9 +20,11 @@ use crate::{
};

/// `Sync` wrapper of `ffi::PyModuleDef`.
#[repr(C)] // Necessary to cast from `*mut ffi::PyModuleDef` to `ModuleDef`
pub struct ModuleDef {
// wrapped in UnsafeCell so that Rust compiler treats this as interior mutability
ffi_def: UnsafeCell<ffi::PyModuleDef>,
ffi_def_initialized: Once,
initializer: ModuleInitializer,
/// Interpreter ID where module was initialized (not applicable on PyPy).
#[cfg(all(
Expand Down Expand Up @@ -49,26 +52,21 @@ impl ModuleDef {
doc: &'static str,
initializer: ModuleInitializer,
) -> Self {
const INIT: ffi::PyModuleDef = ffi::PyModuleDef {
let ffi_def = UnsafeCell::new(ffi::PyModuleDef {
m_base: ffi::PyModuleDef_HEAD_INIT,
m_name: std::ptr::null(),
m_doc: std::ptr::null(),
m_name: name.as_ptr().cast(),
m_doc: doc.as_ptr().cast(),
m_size: 0,
m_methods: std::ptr::null_mut(),
m_slots: std::ptr::null_mut(),
m_traverse: None,
m_clear: None,
m_free: None,
};

let ffi_def = UnsafeCell::new(ffi::PyModuleDef {
m_name: name.as_ptr() as *const _,
m_doc: doc.as_ptr() as *const _,
..INIT
});

ModuleDef {
ffi_def,
ffi_def_initialized: Once::new(),
initializer,
// -1 is never expected to be a valid interpreter ID
#[cfg(all(
Expand All @@ -80,6 +78,30 @@ impl ModuleDef {
module: GILOnceCell::new(),
}
}
pub fn make_def(&'static self) -> *mut ffi::PyModuleDef {
struct ModuleDefSlots([ffi::PyModuleDef_Slot; 1]);
// Safety: this type is an UnsafeCell so the compiler
// will not assume this data is immutable. We have no guarantees with
// whatever the Python interpreter wants to do with this data, sadly.
// We do nothing with it.
unsafe impl Sync for ModuleDefSlots {}

static SLOTS: ModuleDefSlots = ModuleDefSlots([
// SAFETY: a zeroed sentinel required to mark the end
unsafe { std::mem::zeroed() },
]);

let ffi_def = self.ffi_def.get();
self.ffi_def_initialized.call_once(|| unsafe {
// Safety:
// - ffi_def is known to be written to just this once
// - SLOTS will never be used from Rust; the Python API requires *mut PyModuleDef_Slot
(*ffi_def).m_slots = SLOTS.0.as_ptr() as *mut _;
ffi::PyModuleDef_Init(ffi_def);
});
ffi_def
}

/// Builds a module using user given initializer. Used for [`#[pymodule]`][crate::pymodule].
pub fn make_module(&'static self, py: Python<'_>) -> PyResult<Py<PyModule>> {
#[cfg(all(PyPy, not(Py_3_8)))]
Expand Down