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//! PyO3's interior mutability primitive.
//!
//! Rust has strict aliasing rules - you can either have any number of immutable (shared) references or one mutable
//! reference. Python's ownership model is the complete opposite of that - any Python object
//! can be referenced any number of times, and mutation is allowed from any reference.
//!
//! PyO3 deals with these differences by employing the [Interior Mutability]
//! pattern. This requires that PyO3 enforces the borrowing rules and it has two mechanisms for
//! doing so:
//! - Statically it can enforce threadsafe access with the [`Python<'py>`](crate::Python) token.
//! All Rust code holding that token, or anything derived from it, can assume that they have
//! safe access to the Python interpreter's state. For this reason all the native Python objects
//! can be mutated through shared references.
//! - However, methods and functions in Rust usually *do* need `&mut` references. While PyO3 can
//! use the [`Python<'py>`](crate::Python) token to guarantee thread-safe access to them, it cannot
//! statically guarantee uniqueness of `&mut` references. As such those references have to be tracked
//! dynamically at runtime, using [`PyCell`] and the other types defined in this module. This works
//! similar to std's [`RefCell`](std::cell::RefCell) type.
//!
//! # When *not* to use PyCell
//!
//! Usually you can use `&mut` references as method and function receivers and arguments, and you
//! won't need to use [`PyCell`] directly:
//!
//! ```rust
//! use pyo3::prelude::*;
//!
//! #[pyclass]
//! struct Number {
//! inner: u32,
//! }
//!
//! #[pymethods]
//! impl Number {
//! fn increment(&mut self) {
//! self.inner += 1;
//! }
//! }
//! ```
//!
//! The [`#[pymethods]`](crate::pymethods) proc macro will generate this wrapper function (and more),
//! using [`PyCell`] under the hood:
//!
//! ```rust
//! # use pyo3::prelude::*;
//! # #[pyclass]
//! # struct Number {
//! # inner: u32,
//! # }
//! #
//! # #[pymethods]
//! # impl Number {
//! # fn increment(&mut self) {
//! # self.inner += 1;
//! # }
//! # }
//! #
//! // The function which is exported to Python looks roughly like the following
//! unsafe extern "C" fn __pymethod_increment__(
//! _slf: *mut pyo3::ffi::PyObject,
//! _args: *mut pyo3::ffi::PyObject,
//! ) -> *mut pyo3::ffi::PyObject {
//! use :: pyo3 as _pyo3;
//! _pyo3::impl_::trampoline::noargs(_slf, _args, |py, _slf| {
//! let _cell = py
//! .from_borrowed_ptr::<_pyo3::PyAny>(_slf)
//! .downcast::<_pyo3::PyCell<Number>>()?;
//! let mut _ref = _cell.try_borrow_mut()?;
//! let _slf: &mut Number = &mut *_ref;
//! _pyo3::callback::convert(py, Number::increment(_slf))
//! })
//! }
//! ```
//!
//! # When to use PyCell
//! ## Using pyclasses from Rust
//!
//! However, we *do* need [`PyCell`] if we want to call its methods from Rust:
//! ```rust
//! # use pyo3::prelude::*;
//! #
//! # #[pyclass]
//! # struct Number {
//! # inner: u32,
//! # }
//! #
//! # #[pymethods]
//! # impl Number {
//! # fn increment(&mut self) {
//! # self.inner += 1;
//! # }
//! # }
//! # fn main() -> PyResult<()> {
//! Python::with_gil(|py| {
//! let n = Py::new(py, Number { inner: 0 })?;
//!
//! // We borrow the guard and then dereference
//! // it to get a mutable reference to Number
//! let mut guard: PyRefMut<'_, Number> = n.as_ref(py).borrow_mut();
//! let n_mutable: &mut Number = &mut *guard;
//!
//! n_mutable.increment();
//!
//! // To avoid panics we must dispose of the
//! // `PyRefMut` before borrowing again.
//! drop(guard);
//!
//! let n_immutable: &Number = &n.as_ref(py).borrow();
//! assert_eq!(n_immutable.inner, 1);
//!
//! Ok(())
//! })
//! # }
//! ```
//! ## Dealing with possibly overlapping mutable references
//!
//! It is also necessary to use [`PyCell`] if you can receive mutable arguments that may overlap.
//! Suppose the following function that swaps the values of two `Number`s:
//! ```
//! # use pyo3::prelude::*;
//! # #[pyclass]
//! # pub struct Number {
//! # inner: u32,
//! # }
//! #[pyfunction]
//! fn swap_numbers(a: &mut Number, b: &mut Number) {
//! std::mem::swap(&mut a.inner, &mut b.inner);
//! }
//! # fn main() {
//! # Python::with_gil(|py| {
//! # let n = Py::new(py, Number{inner: 35}).unwrap();
//! # let n2 = n.clone_ref(py);
//! # assert!(n.is(&n2));
//! # let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
//! # fun.call1((n, n2)).expect_err("Managed to create overlapping mutable references. Note: this is undefined behaviour.");
//! # });
//! # }
//! ```
//! When users pass in the same `Number` as both arguments, one of the mutable borrows will
//! fail and raise a `RuntimeError`:
//! ```text
//! >>> a = Number()
//! >>> swap_numbers(a, a)
//! Traceback (most recent call last):
//! File "<stdin>", line 1, in <module>
//! RuntimeError: Already borrowed
//! ```
//!
//! It is better to write that function like this:
//! ```rust
//! # use pyo3::prelude::*;
//! # #[pyclass]
//! # pub struct Number {
//! # inner: u32,
//! # }
//! #[pyfunction]
//! fn swap_numbers(a: &PyCell<Number>, b: &PyCell<Number>) {
//! // Check that the pointers are unequal
//! if !a.is(b) {
//! std::mem::swap(&mut a.borrow_mut().inner, &mut b.borrow_mut().inner);
//! } else {
//! // Do nothing - they are the same object, so don't need swapping.
//! }
//! }
//! # fn main() {
//! # // With duplicate numbers
//! # Python::with_gil(|py| {
//! # let n = Py::new(py, Number{inner: 35}).unwrap();
//! # let n2 = n.clone_ref(py);
//! # assert!(n.is(&n2));
//! # let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
//! # fun.call1((n, n2)).unwrap();
//! # });
//! #
//! # // With two different numbers
//! # Python::with_gil(|py| {
//! # let n = Py::new(py, Number{inner: 35}).unwrap();
//! # let n2 = Py::new(py, Number{inner: 42}).unwrap();
//! # assert!(!n.is(&n2));
//! # let fun = pyo3::wrap_pyfunction!(swap_numbers, py).unwrap();
//! # fun.call1((&n, &n2)).unwrap();
//! # let n: u32 = n.borrow(py).inner;
//! # let n2: u32 = n2.borrow(py).inner;
//! # assert_eq!(n, 42);
//! # assert_eq!(n2, 35);
//! # });
//! # }
//! ```
//! See the [guide] for more information.
//!
//! [guide]: https://pyo3.rs/latest/class.html#pycell-and-interior-mutability "PyCell and interior mutability"
//! [Interior Mutability]: https://doc.rust-lang.org/book/ch15-05-interior-mutability.html "RefCell<T> and the Interior Mutability Pattern - The Rust Programming Language"
use crate::exceptions::PyRuntimeError;
use crate::impl_::pyclass::{
PyClassBaseType, PyClassDict, PyClassImpl, PyClassThreadChecker, PyClassWeakRef,
};
use crate::pyclass::{
boolean_struct::{False, True},
PyClass,
};
use crate::pyclass_init::PyClassInitializer;
use crate::type_object::{PyLayout, PySizedLayout};
use crate::types::PyAny;
use crate::{
conversion::{AsPyPointer, FromPyPointer, ToPyObject},
ffi::PyBaseObject_Type,
type_object::get_tp_free,
PyTypeInfo,
};
use crate::{ffi, IntoPy, PyErr, PyNativeType, PyObject, PyResult, Python};
use std::cell::UnsafeCell;
use std::fmt;
use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut};
pub(crate) mod impl_;
use impl_::{GetBorrowChecker, PyClassBorrowChecker, PyClassMutability};
/// Base layout of PyCell.
#[doc(hidden)]
#[repr(C)]
pub struct PyCellBase<T> {
ob_base: T,
}
unsafe impl<T, U> PyLayout<T> for PyCellBase<U> where U: PySizedLayout<T> {}
/// A container type for (mutably) accessing [`PyClass`] values
///
/// `PyCell` autodereferences to [`PyAny`], so you can call `PyAny`'s methods on a `PyCell<T>`.
///
/// # Examples
///
/// This example demonstrates getting a mutable reference of the contained `PyClass`.
/// ```rust
/// use pyo3::prelude::*;
///
/// #[pyclass]
/// struct Number {
/// inner: u32,
/// }
///
/// #[pymethods]
/// impl Number {
/// fn increment(&mut self) {
/// self.inner += 1;
/// }
/// }
///
/// # fn main() -> PyResult<()> {
/// Python::with_gil(|py| {
/// let n = PyCell::new(py, Number { inner: 0 })?;
///
/// let n_mutable: &mut Number = &mut n.borrow_mut();
/// n_mutable.increment();
///
/// Ok(())
/// })
/// # }
/// ```
/// For more information on how, when and why (not) to use `PyCell` please see the
/// [module-level documentation](self).
#[repr(C)]
pub struct PyCell<T: PyClassImpl> {
ob_base: <T::BaseType as PyClassBaseType>::LayoutAsBase,
contents: PyCellContents<T>,
}
#[repr(C)]
pub(crate) struct PyCellContents<T: PyClassImpl> {
pub(crate) value: ManuallyDrop<UnsafeCell<T>>,
pub(crate) borrow_checker: <T::PyClassMutability as PyClassMutability>::Storage,
pub(crate) thread_checker: T::ThreadChecker,
pub(crate) dict: T::Dict,
pub(crate) weakref: T::WeakRef,
}
unsafe impl<T: PyClass> PyNativeType for PyCell<T> {}
impl<T: PyClass> PyCell<T> {
/// Makes a new `PyCell` on the Python heap and return the reference to it.
///
/// In cases where the value in the cell does not need to be accessed immediately after
/// creation, consider [`Py::new`](crate::Py::new) as a more efficient alternative.
pub fn new(py: Python<'_>, value: impl Into<PyClassInitializer<T>>) -> PyResult<&Self> {
unsafe {
let initializer = value.into();
let self_ = initializer.create_cell(py)?;
FromPyPointer::from_owned_ptr_or_err(py, self_ as _)
}
}
/// Immutably borrows the value `T`. This borrow lasts as long as the returned `PyRef` exists.
///
/// For frozen classes, the simpler [`get`][Self::get] is available.
///
/// # Panics
///
/// Panics if the value is currently mutably borrowed. For a non-panicking variant, use
/// [`try_borrow`](#method.try_borrow).
pub fn borrow(&self) -> PyRef<'_, T> {
self.try_borrow().expect("Already mutably borrowed")
}
/// Mutably borrows the value `T`. This borrow lasts as long as the returned `PyRefMut` exists.
///
/// # Panics
///
/// Panics if the value is currently borrowed. For a non-panicking variant, use
/// [`try_borrow_mut`](#method.try_borrow_mut).
pub fn borrow_mut(&self) -> PyRefMut<'_, T>
where
T: PyClass<Frozen = False>,
{
self.try_borrow_mut().expect("Already borrowed")
}
/// Immutably borrows the value `T`, returning an error if the value is currently
/// mutably borrowed. This borrow lasts as long as the returned `PyRef` exists.
///
/// This is the non-panicking variant of [`borrow`](#method.borrow).
///
/// For frozen classes, the simpler [`get`][Self::get] is available.
///
/// # Examples
///
/// ```
/// # use pyo3::prelude::*;
/// #[pyclass]
/// struct Class {}
///
/// Python::with_gil(|py| {
/// let c = PyCell::new(py, Class {}).unwrap();
/// {
/// let m = c.borrow_mut();
/// assert!(c.try_borrow().is_err());
/// }
///
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow().is_ok());
/// }
/// });
/// ```
pub fn try_borrow(&self) -> Result<PyRef<'_, T>, PyBorrowError> {
self.ensure_threadsafe();
self.borrow_checker()
.try_borrow()
.map(|_| PyRef { inner: self })
}
/// Mutably borrows the value `T`, returning an error if the value is currently borrowed.
/// This borrow lasts as long as the returned `PyRefMut` exists.
///
/// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).
///
/// # Examples
///
/// ```
/// # use pyo3::prelude::*;
/// #[pyclass]
/// struct Class {}
/// Python::with_gil(|py| {
/// let c = PyCell::new(py, Class {}).unwrap();
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow_mut().is_err());
/// }
///
/// assert!(c.try_borrow_mut().is_ok());
/// });
/// ```
pub fn try_borrow_mut(&self) -> Result<PyRefMut<'_, T>, PyBorrowMutError>
where
T: PyClass<Frozen = False>,
{
self.ensure_threadsafe();
self.borrow_checker()
.try_borrow_mut()
.map(|_| PyRefMut { inner: self })
}
/// Immutably borrows the value `T`, returning an error if the value is
/// currently mutably borrowed.
///
/// # Safety
///
/// This method is unsafe because it does not return a `PyRef`,
/// thus leaving the borrow flag untouched. Mutably borrowing the `PyCell`
/// while the reference returned by this method is alive is undefined behaviour.
///
/// # Examples
///
/// ```
/// # use pyo3::prelude::*;
/// #[pyclass]
/// struct Class {}
/// Python::with_gil(|py| {
/// let c = PyCell::new(py, Class {}).unwrap();
///
/// {
/// let m = c.borrow_mut();
/// assert!(unsafe { c.try_borrow_unguarded() }.is_err());
/// }
///
/// {
/// let m = c.borrow();
/// assert!(unsafe { c.try_borrow_unguarded() }.is_ok());
/// }
/// });
/// ```
pub unsafe fn try_borrow_unguarded(&self) -> Result<&T, PyBorrowError> {
self.ensure_threadsafe();
self.borrow_checker()
.try_borrow_unguarded()
.map(|_: ()| &*self.contents.value.get())
}
/// Provide an immutable borrow of the value `T` without acquiring the GIL.
///
/// This is available if the class is [`frozen`][macro@crate::pyclass] and [`Sync`].
///
/// While the GIL is usually required to get access to `&PyCell<T>`,
/// compared to [`borrow`][Self::borrow] or [`try_borrow`][Self::try_borrow]
/// this avoids any thread or borrow checking overhead at runtime.
///
/// # Examples
///
/// ```
/// use std::sync::atomic::{AtomicUsize, Ordering};
/// # use pyo3::prelude::*;
///
/// #[pyclass(frozen)]
/// struct FrozenCounter {
/// value: AtomicUsize,
/// }
///
/// Python::with_gil(|py| {
/// let counter = FrozenCounter { value: AtomicUsize::new(0) };
///
/// let cell = PyCell::new(py, counter).unwrap();
///
/// cell.get().value.fetch_add(1, Ordering::Relaxed);
/// });
/// ```
pub fn get(&self) -> &T
where
T: PyClass<Frozen = True> + Sync,
{
// SAFETY: The class itself is frozen and `Sync` and we do not access anything but `self.contents.value`.
unsafe { &*self.get_ptr() }
}
/// Replaces the wrapped value with a new one, returning the old value.
///
/// # Panics
///
/// Panics if the value is currently borrowed.
#[inline]
pub fn replace(&self, t: T) -> T
where
T: PyClass<Frozen = False>,
{
std::mem::replace(&mut *self.borrow_mut(), t)
}
/// Replaces the wrapped value with a new one computed from `f`, returning the old value.
///
/// # Panics
///
/// Panics if the value is currently borrowed.
pub fn replace_with<F: FnOnce(&mut T) -> T>(&self, f: F) -> T
where
T: PyClass<Frozen = False>,
{
let mut_borrow = &mut *self.borrow_mut();
let replacement = f(mut_borrow);
std::mem::replace(mut_borrow, replacement)
}
/// Swaps the wrapped value of `self` with the wrapped value of `other`.
///
/// # Panics
///
/// Panics if the value in either `PyCell` is currently borrowed.
#[inline]
pub fn swap(&self, other: &Self)
where
T: PyClass<Frozen = False>,
{
std::mem::swap(&mut *self.borrow_mut(), &mut *other.borrow_mut())
}
pub(crate) fn get_ptr(&self) -> *mut T {
self.contents.value.get()
}
/// Gets the offset of the dictionary from the start of the struct in bytes.
pub(crate) fn dict_offset() -> ffi::Py_ssize_t {
use memoffset::offset_of;
use std::convert::TryInto;
let offset = offset_of!(PyCell<T>, contents) + offset_of!(PyCellContents<T>, dict);
// Py_ssize_t may not be equal to isize on all platforms
#[allow(clippy::useless_conversion)]
offset.try_into().expect("offset should fit in Py_ssize_t")
}
/// Gets the offset of the weakref list from the start of the struct in bytes.
pub(crate) fn weaklist_offset() -> ffi::Py_ssize_t {
use memoffset::offset_of;
use std::convert::TryInto;
let offset = offset_of!(PyCell<T>, contents) + offset_of!(PyCellContents<T>, weakref);
// Py_ssize_t may not be equal to isize on all platforms
#[allow(clippy::useless_conversion)]
offset.try_into().expect("offset should fit in Py_ssize_t")
}
}
impl<T: PyClassImpl> PyCell<T> {
fn borrow_checker(&self) -> &<T::PyClassMutability as PyClassMutability>::Checker {
T::PyClassMutability::borrow_checker(self)
}
}
unsafe impl<T: PyClassImpl> PyLayout<T> for PyCell<T> {}
impl<T: PyClass> PySizedLayout<T> for PyCell<T> {}
impl<T: PyClass> AsPyPointer for PyCell<T> {
fn as_ptr(&self) -> *mut ffi::PyObject {
(self as *const _) as *mut _
}
}
impl<T: PyClass> ToPyObject for &PyCell<T> {
fn to_object(&self, py: Python<'_>) -> PyObject {
unsafe { PyObject::from_borrowed_ptr(py, self.as_ptr()) }
}
}
impl<T: PyClass> AsRef<PyAny> for PyCell<T> {
fn as_ref(&self) -> &PyAny {
unsafe { self.py().from_borrowed_ptr(self.as_ptr()) }
}
}
impl<T: PyClass> Deref for PyCell<T> {
type Target = PyAny;
fn deref(&self) -> &PyAny {
unsafe { self.py().from_borrowed_ptr(self.as_ptr()) }
}
}
impl<T: PyClass + fmt::Debug> fmt::Debug for PyCell<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.try_borrow() {
Ok(borrow) => f.debug_struct("RefCell").field("value", &borrow).finish(),
Err(_) => {
struct BorrowedPlaceholder;
impl fmt::Debug for BorrowedPlaceholder {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("<borrowed>")
}
}
f.debug_struct("RefCell")
.field("value", &BorrowedPlaceholder)
.finish()
}
}
}
}
/// A wrapper type for an immutably borrowed value from a [`PyCell`]`<T>`.
///
/// See the [`PyCell`] documentation for more information.
///
/// # Examples
///
/// You can use `PyRef` as an alternative to a `&self` receiver when
/// - you need to access the pointer of the `PyCell`, or
/// - you want to get a super class.
/// ```
/// # use pyo3::prelude::*;
/// #[pyclass(subclass)]
/// struct Parent {
/// basename: &'static str,
/// }
///
/// #[pyclass(extends=Parent)]
/// struct Child {
/// name: &'static str,
/// }
///
/// #[pymethods]
/// impl Child {
/// #[new]
/// fn new() -> (Self, Parent) {
/// (Child { name: "Caterpillar" }, Parent { basename: "Butterfly" })
/// }
///
/// fn format(slf: PyRef<'_, Self>) -> String {
/// // We can get *mut ffi::PyObject from PyRef
/// use pyo3::AsPyPointer;
/// let refcnt = unsafe { pyo3::ffi::Py_REFCNT(slf.as_ptr()) };
/// // We can get &Self::BaseType by as_ref
/// let basename = slf.as_ref().basename;
/// format!("{}(base: {}, cnt: {})", slf.name, basename, refcnt)
/// }
/// }
/// # Python::with_gil(|py| {
/// # let sub = PyCell::new(py, Child::new()).unwrap();
/// # pyo3::py_run!(py, sub, "assert sub.format() == 'Caterpillar(base: Butterfly, cnt: 3)'");
/// # });
/// ```
///
/// See the [module-level documentation](self) for more information.
pub struct PyRef<'p, T: PyClass> {
inner: &'p PyCell<T>,
}
impl<'p, T: PyClass> PyRef<'p, T> {
/// Returns a `Python` token that is bound to the lifetime of the `PyRef`.
pub fn py(&self) -> Python<'p> {
self.inner.py()
}
}
impl<'p, T, U> AsRef<U> for PyRef<'p, T>
where
T: PyClass<BaseType = U>,
U: PyClass,
{
fn as_ref(&self) -> &T::BaseType {
unsafe { &*self.inner.ob_base.get_ptr() }
}
}
impl<'p, T, U> PyRef<'p, T>
where
T: PyClass<BaseType = U>,
U: PyClass,
{
/// Gets a `PyRef<T::BaseType>`.
///
/// While `as_ref()` returns a reference of type `&T::BaseType`, this cannot be
/// used to get the base of `T::BaseType`.
///
/// But with the help of this method, you can get hold of instances of the
/// super-superclass when needed.
///
/// # Examples
/// ```
/// # use pyo3::prelude::*;
/// #[pyclass(subclass)]
/// struct Base1 {
/// name1: &'static str,
/// }
///
/// #[pyclass(extends=Base1, subclass)]
/// struct Base2 {
/// name2: &'static str,
/// }
///
/// #[pyclass(extends=Base2)]
/// struct Sub {
/// name3: &'static str,
/// }
///
/// #[pymethods]
/// impl Sub {
/// #[new]
/// fn new() -> PyClassInitializer<Self> {
/// PyClassInitializer::from(Base1 { name1: "base1" })
/// .add_subclass(Base2 { name2: "base2" })
/// .add_subclass(Self { name3: "sub" })
/// }
/// fn name(slf: PyRef<'_, Self>) -> String {
/// let subname = slf.name3;
/// let super_ = slf.into_super();
/// format!("{} {} {}", super_.as_ref().name1, super_.name2, subname)
/// }
/// }
/// # Python::with_gil(|py| {
/// # let sub = PyCell::new(py, Sub::new()).unwrap();
/// # pyo3::py_run!(py, sub, "assert sub.name() == 'base1 base2 sub'")
/// # });
/// ```
pub fn into_super(self) -> PyRef<'p, U> {
let PyRef { inner } = self;
std::mem::forget(self);
PyRef {
inner: &inner.ob_base,
}
}
}
impl<'p, T: PyClass> Deref for PyRef<'p, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
unsafe { &*self.inner.get_ptr() }
}
}
impl<'p, T: PyClass> Drop for PyRef<'p, T> {
fn drop(&mut self) {
self.inner.borrow_checker().release_borrow()
}
}
impl<T: PyClass> IntoPy<PyObject> for PyRef<'_, T> {
fn into_py(self, py: Python<'_>) -> PyObject {
unsafe { PyObject::from_borrowed_ptr(py, self.inner.as_ptr()) }
}
}
impl<'a, T: PyClass> std::convert::TryFrom<&'a PyCell<T>> for crate::PyRef<'a, T> {
type Error = PyBorrowError;
fn try_from(cell: &'a crate::PyCell<T>) -> Result<Self, Self::Error> {
cell.try_borrow()
}
}
impl<'a, T: PyClass> AsPyPointer for PyRef<'a, T> {
fn as_ptr(&self) -> *mut ffi::PyObject {
self.inner.as_ptr()
}
}
impl<T: PyClass + fmt::Debug> fmt::Debug for PyRef<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, f)
}
}
/// A wrapper type for a mutably borrowed value from a[`PyCell`]`<T>`.
///
/// See the [module-level documentation](self) for more information.
pub struct PyRefMut<'p, T: PyClass<Frozen = False>> {
inner: &'p PyCell<T>,
}
impl<'p, T: PyClass<Frozen = False>> PyRefMut<'p, T> {
/// Returns a `Python` token that is bound to the lifetime of the `PyRefMut`.
pub fn py(&self) -> Python<'p> {
self.inner.py()
}
}
impl<'p, T, U> AsRef<U> for PyRefMut<'p, T>
where
T: PyClass<BaseType = U, Frozen = False>,
U: PyClass<Frozen = False>,
{
fn as_ref(&self) -> &T::BaseType {
unsafe { &*self.inner.ob_base.get_ptr() }
}
}
impl<'p, T, U> AsMut<U> for PyRefMut<'p, T>
where
T: PyClass<BaseType = U, Frozen = False>,
U: PyClass<Frozen = False>,
{
fn as_mut(&mut self) -> &mut T::BaseType {
unsafe { &mut *self.inner.ob_base.get_ptr() }
}
}
impl<'p, T, U> PyRefMut<'p, T>
where
T: PyClass<BaseType = U, Frozen = False>,
U: PyClass<Frozen = False>,
{
/// Gets a `PyRef<T::BaseType>`.
///
/// See [`PyRef::into_super`] for more.
pub fn into_super(self) -> PyRefMut<'p, U> {
let PyRefMut { inner } = self;
std::mem::forget(self);
PyRefMut {
inner: &inner.ob_base,
}
}
}
impl<'p, T: PyClass<Frozen = False>> Deref for PyRefMut<'p, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
unsafe { &*self.inner.get_ptr() }
}
}
impl<'p, T: PyClass<Frozen = False>> DerefMut for PyRefMut<'p, T> {
#[inline]
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.inner.get_ptr() }
}
}
impl<'p, T: PyClass<Frozen = False>> Drop for PyRefMut<'p, T> {
fn drop(&mut self) {
self.inner.borrow_checker().release_borrow_mut()
}
}
impl<T: PyClass<Frozen = False>> IntoPy<PyObject> for PyRefMut<'_, T> {
fn into_py(self, py: Python<'_>) -> PyObject {
unsafe { PyObject::from_borrowed_ptr(py, self.inner.as_ptr()) }
}
}
impl<'a, T: PyClass<Frozen = False>> AsPyPointer for PyRefMut<'a, T> {
fn as_ptr(&self) -> *mut ffi::PyObject {
self.inner.as_ptr()
}
}
impl<'a, T: PyClass<Frozen = False>> std::convert::TryFrom<&'a PyCell<T>>
for crate::PyRefMut<'a, T>
{
type Error = PyBorrowMutError;
fn try_from(cell: &'a crate::PyCell<T>) -> Result<Self, Self::Error> {
cell.try_borrow_mut()
}
}
impl<T: PyClass<Frozen = False> + fmt::Debug> fmt::Debug for PyRefMut<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(self.deref(), f)
}
}
/// An error type returned by [`PyCell::try_borrow`].
///
/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
pub struct PyBorrowError {
_private: (),
}
impl fmt::Debug for PyBorrowError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("PyBorrowError").finish()
}
}
impl fmt::Display for PyBorrowError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt("Already mutably borrowed", f)
}
}
impl From<PyBorrowError> for PyErr {
fn from(other: PyBorrowError) -> Self {
PyRuntimeError::new_err(other.to_string())
}
}
/// An error type returned by [`PyCell::try_borrow_mut`].
///
/// If this error is allowed to bubble up into Python code it will raise a `RuntimeError`.
pub struct PyBorrowMutError {
_private: (),
}
impl fmt::Debug for PyBorrowMutError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("PyBorrowMutError").finish()
}
}
impl fmt::Display for PyBorrowMutError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt("Already borrowed", f)
}
}
impl From<PyBorrowMutError> for PyErr {
fn from(other: PyBorrowMutError) -> Self {
PyRuntimeError::new_err(other.to_string())
}
}
#[doc(hidden)]
pub trait PyCellLayout<T>: PyLayout<T> {
fn ensure_threadsafe(&self);
/// Implementation of tp_dealloc.
/// # Safety
/// - slf must be a valid pointer to an instance of a T or a subclass.
/// - slf must not be used after this call (as it will be freed).
unsafe fn tp_dealloc(py: Python<'_>, slf: *mut ffi::PyObject);
}
impl<T, U> PyCellLayout<T> for PyCellBase<U>
where
U: PySizedLayout<T>,
T: PyTypeInfo,
{
fn ensure_threadsafe(&self) {}
unsafe fn tp_dealloc(py: Python<'_>, slf: *mut ffi::PyObject) {
// For `#[pyclass]` types which inherit from PyAny, we can just call tp_free
if T::type_object_raw(py) == &mut PyBaseObject_Type {
return get_tp_free(ffi::Py_TYPE(slf))(slf as _);
}
// More complex native types (e.g. `extends=PyDict`) require calling the base's dealloc.
#[cfg(not(Py_LIMITED_API))]
{
if let Some(dealloc) = (*T::type_object_raw(py)).tp_dealloc {
dealloc(slf as _);
} else {
get_tp_free(ffi::Py_TYPE(slf))(slf as _);
}
}
#[cfg(Py_LIMITED_API)]
unreachable!("subclassing native types is not possible with the `abi3` feature");
}
}
impl<T: PyClassImpl> PyCellLayout<T> for PyCell<T>
where
<T::BaseType as PyClassBaseType>::LayoutAsBase: PyCellLayout<T::BaseType>,
{
fn ensure_threadsafe(&self) {
self.contents.thread_checker.ensure();
self.ob_base.ensure_threadsafe();
}
unsafe fn tp_dealloc(py: Python<'_>, slf: *mut ffi::PyObject) {
// Safety: Python only calls tp_dealloc when no references to the object remain.
let cell = &mut *(slf as *mut PyCell<T>);
if cell.contents.thread_checker.can_drop(py) {
ManuallyDrop::drop(&mut cell.contents.value);
}
cell.contents.dict.clear_dict(py);
cell.contents.weakref.clear_weakrefs(slf, py);
<T::BaseType as PyClassBaseType>::LayoutAsBase::tp_dealloc(py, slf)
}
}
#[cfg(test)]
#[cfg(feature = "macros")]
mod tests {
use super::*;
#[crate::pyclass]
#[pyo3(crate = "crate")]
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
struct SomeClass(i32);
#[test]
fn pycell_replace() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
assert_eq!(*cell.borrow(), SomeClass(0));
let previous = cell.replace(SomeClass(123));
assert_eq!(previous, SomeClass(0));
assert_eq!(*cell.borrow(), SomeClass(123));
})
}
#[test]
#[should_panic(expected = "Already borrowed: PyBorrowMutError")]
fn pycell_replace_panic() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
let _guard = cell.borrow();
cell.replace(SomeClass(123));
})
}
#[test]
fn pycell_replace_with() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
assert_eq!(*cell.borrow(), SomeClass(0));
let previous = cell.replace_with(|value| {
*value = SomeClass(2);
SomeClass(123)
});
assert_eq!(previous, SomeClass(2));
assert_eq!(*cell.borrow(), SomeClass(123));
})
}
#[test]
#[should_panic(expected = "Already borrowed: PyBorrowMutError")]
fn pycell_replace_with_panic() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
let _guard = cell.borrow();
cell.replace_with(|_| SomeClass(123));
})
}
#[test]
fn pycell_swap() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
let cell2 = PyCell::new(py, SomeClass(123)).unwrap();
assert_eq!(*cell.borrow(), SomeClass(0));
assert_eq!(*cell2.borrow(), SomeClass(123));
cell.swap(cell2);
assert_eq!(*cell.borrow(), SomeClass(123));
assert_eq!(*cell2.borrow(), SomeClass(0));
})
}
#[test]
#[should_panic(expected = "Already borrowed: PyBorrowMutError")]
fn pycell_swap_panic() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
let cell2 = PyCell::new(py, SomeClass(123)).unwrap();
let _guard = cell.borrow();
cell.swap(cell2);
})
}
#[test]
#[should_panic(expected = "Already borrowed: PyBorrowMutError")]
fn pycell_swap_panic_other_borrowed() {
Python::with_gil(|py| {
let cell = PyCell::new(py, SomeClass(0)).unwrap();
let cell2 = PyCell::new(py, SomeClass(123)).unwrap();
let _guard = cell2.borrow();
cell.swap(cell2);
})
}
}