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Add pyo3::once_cell::GILOnceCell

This commit is contained in:
David Hewitt 2020-06-14 16:29:40 +01:00
parent 390ff5f17f
commit a1dbfa8c8c
14 changed files with 270 additions and 178 deletions
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3
CHANGELOG.md
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@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
### Added
- Add FFI definition `PyObject_AsFileDescriptor` [#938](https://github.com/PyO3/pyo3/pull/938)
- Add `PyByteArray::data`, `PyByteArray::as_bytes`, and `PyByteArray::as_bytes_mut`. [#967](https://github.com/PyO3/pyo3/pull/967)
- Add `GILOnceCell` to use in situations where `lazy_static` or `once_cell` can deadlock. [#975](https://github.com/PyO3/pyo3/pull/975)
- Add `Py::borrow`, `Py::borrow_mut`, `Py::try_borrow`, and `Py::try_borrow_mut` for accessing `#[pyclass]` values. [#976](https://github.com/PyO3/pyo3/pull/976)
### Changed
@ -19,12 +20,14 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
- Change signature of `PyTypeObject::type_object()` - now takes `Python` argument and returns `&PyType`. [#970](https://github.com/PyO3/pyo3/pull/970)
- Change return type of `PyTuple::slice()` and `PyTuple::split_from()` from `Py<PyTuple>` to `&PyTuple`. [#970](https://github.com/PyO3/pyo3/pull/970)
- Change return type of `PyTuple::as_slice` to `&[&PyAny]`. [#971](https://github.com/PyO3/pyo3/pull/971)
- Rename `PyTypeInfo::type_object` to `type_object_raw`, and add `Python` argument. [#975](https://github.com/PyO3/pyo3/pull/975)
- Update `num-complex` optional dependendency from `0.2` to `0.3`. [#977](https://github.com/PyO3/pyo3/pull/977)
- Update `num-bigint` optional dependendency from `0.2` to `0.3`. [#978](https://github.com/PyO3/pyo3/pull/978)
- `#[pyproto]` is re-implemented without specialization. [#961](https://github.com/PyO3/pyo3/pull/961)
### Removed
- Remove `ManagedPyRef` (unused, and needs specialization) [#930](https://github.com/PyO3/pyo3/pull/930)
- Disable `#[classattr]` where the class attribute is the same type as the class. (This may be re-enabled in the future; the previous implemenation was unsound.) [#975](https://github.com/PyO3/pyo3/pull/975)
### Fixed
- Fix passing explicit `None` to `Option<T>` argument `#[pyfunction]` with a default value. [#936](https://github.com/PyO3/pyo3/pull/936)

1
guide/src/SUMMARY.md
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@ -12,6 +12,7 @@
- [Advanced Topics](advanced.md)
- [Building and Distribution](building_and_distribution.md)
- [PyPy support](pypy.md)
- [FAQ & Troubleshooting](faq.md)
- [Appendix A: PyO3 and rust-cpython](rust_cpython.md)
- [Appendix B: Migration Guide](migration.md)
- [Appendix C: Trait bounds](trait_bounds.md)

9
guide/src/class.md
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@ -565,6 +565,11 @@ impl MyClass {
}
```
Note that defining a class attribute of the same type as the class will make the class unusable.
Attempting to use the class will cause a panic reading `Recursive evaluation of type_object`.
As an alternative, if having the attribute on instances is acceptable, create a `#[getter]` which
uses a `GILOnceCell` to cache the attribute value. Or add the attribute to a module instead.
## Callable objects
To specify a custom `__call__` method for a custom class, the method needs to be annotated with
@ -922,10 +927,10 @@ unsafe impl pyo3::PyTypeInfo for MyClass {
const FLAGS: usize = 0;
#[inline]
fn type_object() -> &'static pyo3::ffi::PyTypeObject {
fn type_object_raw(py: pyo3::Python) -> &'static pyo3::ffi::PyTypeObject {
use pyo3::type_object::LazyStaticType;
static TYPE_OBJECT: LazyStaticType = LazyStaticType::new();
TYPE_OBJECT.get_or_init::<Self>()
TYPE_OBJECT.get_or_init::<Self>(py)
}
}

16
guide/src/faq.md Normal file
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@ -0,0 +1,16 @@
# Frequently Asked Questions / Troubleshooting
## I'm experiencing deadlocks using PyO3 with lazy_static or once_cell!
`lazy_static` and `once_cell::sync` both use locks to ensure that initialization is performed only by a single thread. Because the Python GIL is an additional lock this can lead to deadlocks in the following way:
1. A thread (thread A) which has acquired the Python GIL starts initialization of a `lazy_static` value.
2. The initialization code calls some Python API which temporarily releases the GIL e.g. `Python::import`.
3. Another thread (thread B) acquires the Python GIL and attempts to access the same `lazy_static` value.
4. Thread B is blocked, because it waits for `lazy_static`'s initialization to lock to release.
5. Thread A is blocked, because it waits to re-aquire the GIL which thread B still holds.
6. Deadlock.
PyO3 provides a struct [`GILOnceCell`] which works equivalently to `OnceCell` but relies solely on the Python GIL for thread safety. This means it can be used in place of `lazy_static` or `once_cell` where you are experiencing the deadlock described above. See the documentation for [`GILOnceCell`] for an example how to use it.
[`GILOnceCell`]: https://docs.rs/pyo3/latest/pyo3/once_cell/struct.GILOnceCell.html

4
pyo3-derive-backend/src/pyclass.rs
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@ -401,10 +401,10 @@ fn impl_class(
const FLAGS: usize = #(#flags)|* | #extended;
#[inline]
fn type_object() -> &'static pyo3::ffi::PyTypeObject {
fn type_object_raw(py: pyo3::Python) -> &'static pyo3::ffi::PyTypeObject {
use pyo3::type_object::LazyStaticType;
static TYPE_OBJECT: LazyStaticType = LazyStaticType::new();
TYPE_OBJECT.get_or_init::<Self>()
TYPE_OBJECT.get_or_init::<Self>(py)
}
}

69
src/exceptions.rs
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@ -90,28 +90,27 @@ macro_rules! import_exception_type_object {
($module: expr, $name: ident) => {
unsafe impl $crate::type_object::PyTypeObject for $name {
fn type_object(py: $crate::Python) -> &$crate::types::PyType {
use $crate::type_object::LazyHeapType;
static TYPE_OBJECT: LazyHeapType = LazyHeapType::new();
use $crate::once_cell::GILOnceCell;
use $crate::AsPyRef;
static TYPE_OBJECT: GILOnceCell<$crate::Py<$crate::types::PyType>> =
GILOnceCell::new();
let ptr = TYPE_OBJECT.get_or_init(|py| {
let imp = py
.import(stringify!($module))
.expect(concat!("Can not import module: ", stringify!($module)));
let cls = imp.get(stringify!($name)).expect(concat!(
"Can not load exception class: {}.{}",
stringify!($module),
".",
stringify!($name)
));
TYPE_OBJECT
.get_or_init(py, || {
let imp = py
.import(stringify!($module))
.expect(concat!("Can not import module: ", stringify!($module)));
let cls = imp.get(stringify!($name)).expect(concat!(
"Can not load exception class: {}.{}",
stringify!($module),
".",
stringify!($name)
));
unsafe {
std::ptr::NonNull::new_unchecked(
$crate::IntoPyPointer::into_ptr(cls) as *mut _
)
}
});
unsafe { py.from_borrowed_ptr(ptr.as_ptr() as *mut $crate::ffi::PyObject) }
cls.extract()
.expect("Imported exception should be a type object")
})
.as_ref(py)
}
}
};
@ -174,19 +173,25 @@ macro_rules! create_exception_type_object {
($module: ident, $name: ident, $base: ty) => {
unsafe impl $crate::type_object::PyTypeObject for $name {
fn type_object(py: $crate::Python) -> &$crate::types::PyType {
use $crate::type_object::LazyHeapType;
static TYPE_OBJECT: LazyHeapType = LazyHeapType::new();
use $crate::once_cell::GILOnceCell;
use $crate::AsPyRef;
static TYPE_OBJECT: GILOnceCell<$crate::Py<$crate::types::PyType>> =
GILOnceCell::new();
let ptr = TYPE_OBJECT.get_or_init(|py| {
$crate::PyErr::new_type(
py,
concat!(stringify!($module), ".", stringify!($name)),
Some(py.get_type::<$base>()),
None,
)
});
unsafe { py.from_borrowed_ptr(ptr.as_ptr() as *mut $crate::ffi::PyObject) }
TYPE_OBJECT
.get_or_init(py, || unsafe {
$crate::Py::from_owned_ptr(
py,
$crate::PyErr::new_type(
py,
concat!(stringify!($module), ".", stringify!($name)),
Some(py.get_type::<$base>()),
None,
)
.as_ptr() as *mut $crate::ffi::PyObject,
)
})
.as_ref(py)
}
}
};

70
src/ffi/datetime.rs
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@ -14,10 +14,10 @@
use crate::ffi::Py_hash_t;
use crate::ffi::{PyObject, PyTypeObject};
use crate::ffi::{PyObject_TypeCheck, Py_TYPE};
use crate::once_cell::GILOnceCell;
use crate::Python;
use std::ops::Deref;
use std::os::raw::{c_char, c_int, c_uchar};
use std::ptr;
use std::sync::Once;
#[cfg(not(PyPy))]
use {crate::ffi::PyCapsule_Import, std::ffi::CString};
@ -196,29 +196,9 @@ pub struct PyDateTime_Delta {
pub microseconds: c_int,
}
// C API Capsule
// Note: This is "roll-your-own" lazy-static implementation is necessary because
// of the interaction between the call_once locks and the GIL. It turns out that
// calling PyCapsule_Import releases and re-acquires the GIL during the import,
// so if you have two threads attempting to use the PyDateTimeAPI singleton
// under the GIL, it causes a deadlock; what happens is:
//
// Thread 1 acquires GIL
// Thread 1 acquires the call_once lock
// Thread 1 calls PyCapsule_Import, thus releasing the GIL
// Thread 2 acquires the GIL
// Thread 2 blocks waiting for the call_once lock
// Thread 1 blocks waiting for the GIL
//
// However, Python's import mechanism acquires a module-specific lock around
// each import call, so all call importing datetime will return the same
// object, making the call_once lock superfluous. As such, we can weaken
// the guarantees of the cache, such that PyDateTime_IMPORT can be called
// until __PY_DATETIME_API_UNSAFE_CACHE is populated, which will happen exactly
// one time. So long as PyDateTime_IMPORT has no side effects (it should not),
// this will be at most a slight waste of resources.
static PY_DATETIME_API_ONCE: Once = Once::new();
static mut PY_DATETIME_API_UNSAFE_CACHE: *const PyDateTime_CAPI = ptr::null();
// Python already shares this object between threads, so it's no more evil for us to do it too!
unsafe impl Sync for PyDateTime_CAPI {}
static PY_DATETIME_API: GILOnceCell<&'static PyDateTime_CAPI> = GILOnceCell::new();
#[derive(Debug)]
pub struct PyDateTimeAPI {
@ -233,13 +213,7 @@ impl Deref for PyDateTimeAPI {
type Target = PyDateTime_CAPI;
fn deref(&self) -> &'static PyDateTime_CAPI {
unsafe {
if !PY_DATETIME_API_UNSAFE_CACHE.is_null() {
&(*PY_DATETIME_API_UNSAFE_CACHE)
} else {
PyDateTime_IMPORT()
}
}
unsafe { PyDateTime_IMPORT() }
}
}
@ -251,25 +225,27 @@ impl Deref for PyDateTimeAPI {
/// Use this function only if you want to eagerly load the datetime module,
/// such as if you do not want the first call to a datetime function to be
/// slightly slower than subsequent calls.
///
/// # Safety
/// The Python GIL must be held.
pub unsafe fn PyDateTime_IMPORT() -> &'static PyDateTime_CAPI {
// PyPy expects the C-API to be initialized via PyDateTime_Import, so trying to use
// `PyCapsule_Import` will behave unexpectedly in pypy.
#[cfg(PyPy)]
let py_datetime_c_api = PyDateTime_Import();
let py = Python::assume_gil_acquired();
PY_DATETIME_API.get_or_init(py, || {
// PyPy expects the C-API to be initialized via PyDateTime_Import, so trying to use
// `PyCapsule_Import` will behave unexpectedly in pypy.
#[cfg(PyPy)]
let py_datetime_c_api = PyDateTime_Import();
#[cfg(not(PyPy))]
let py_datetime_c_api = {
// PyDateTime_CAPSULE_NAME is a macro in C
let PyDateTime_CAPSULE_NAME = CString::new("datetime.datetime_CAPI").unwrap();
#[cfg(not(PyPy))]
let py_datetime_c_api = {
// PyDateTime_CAPSULE_NAME is a macro in C
let PyDateTime_CAPSULE_NAME = CString::new("datetime.datetime_CAPI").unwrap();
PyCapsule_Import(PyDateTime_CAPSULE_NAME.as_ptr(), 1) as *const PyDateTime_CAPI
};
&*(PyCapsule_Import(PyDateTime_CAPSULE_NAME.as_ptr(), 1) as *const PyDateTime_CAPI)
};
PY_DATETIME_API_ONCE.call_once(move || {
PY_DATETIME_API_UNSAFE_CACHE = py_datetime_c_api;
});
&(*PY_DATETIME_API_UNSAFE_CACHE)
py_datetime_c_api
})
}
/// Type Check macros

8
src/freelist.rs
View File

@ -72,12 +72,12 @@ impl<T> PyClassAlloc for T
where
T: PyTypeInfo + PyClassWithFreeList,
{
unsafe fn alloc(_py: Python) -> *mut Self::Layout {
unsafe fn alloc(py: Python) -> *mut Self::Layout {
if let Some(obj) = <Self as PyClassWithFreeList>::get_free_list().pop() {
ffi::PyObject_Init(obj, <Self as PyTypeInfo>::type_object() as *const _ as _);
ffi::PyObject_Init(obj, Self::type_object_raw(py) as *const _ as _);
obj as _
} else {
crate::pyclass::default_alloc::<Self>() as _
crate::pyclass::default_alloc::<Self>(py) as _
}
}
@ -90,7 +90,7 @@ where
}
if let Some(obj) = <Self as PyClassWithFreeList>::get_free_list().insert(obj) {
match Self::type_object().tp_free {
match Self::type_object_raw(py).tp_free {
Some(free) => free(obj as *mut c_void),
None => tp_free_fallback(obj),
}

1
src/lib.rs
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@ -184,6 +184,7 @@ mod instance;
mod internal_tricks;
pub mod marshal;
mod object;
pub mod once_cell;
pub mod panic;
pub mod prelude;
pub mod pycell;

100
src/once_cell.rs Normal file
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@ -0,0 +1,100 @@
use crate::Python;
use std::cell::UnsafeCell;
/// A write-once cell similar to [`once_cell::OnceCell`](https://docs.rs/once_cell/1.4.0/once_cell/).
///
/// Unlike `once_cell::sync` which blocks threads to achieve thread safety, this implementation
/// uses the Python GIL to mediate concurrent access. This helps in cases where `once_sync` or
/// `lazy_static`'s synchronization strategy can lead to deadlocks when interacting with the Python
/// GIL. For an example, see [the FAQ section](https://pyo3.rs/master/faq.html) of the guide.
///
/// # Example
///
/// The following example shows how to use `GILOnceCell` to share a reference to a Python list
/// between threads:
///
/// ```
/// use pyo3::prelude::*;
/// use pyo3::types::PyList;
/// use pyo3::once_cell::GILOnceCell;
///
/// static LIST_CELL: GILOnceCell<Py<PyList>> = GILOnceCell::new();
///
/// pub fn get_shared_list(py: Python) -> &PyList {
/// LIST_CELL
/// .get_or_init(py, || PyList::empty(py).into())
/// .as_ref(py)
/// }
/// # let gil = Python::acquire_gil();
/// # let py = gil.python();
/// # assert_eq!(get_shared_list(py).len(), 0 );
/// ```
pub struct GILOnceCell<T>(UnsafeCell<Option<T>>);
// T: Send is needed for Sync because the thread which drops the GILOnceCell can be different
// to the thread which fills it.
unsafe impl<T: Send + Sync> Sync for GILOnceCell<T> {}
unsafe impl<T: Send> Send for GILOnceCell<T> {}
impl<T> GILOnceCell<T> {
/// Create a `GILOnceCell` which does not yet contain a value.
pub const fn new() -> Self {
Self(UnsafeCell::new(None))
}
/// Get a reference to the contained value, or `None` if the cell has not yet been written.
pub fn get(&self, _py: Python) -> Option<&T> {
// Safe because if the cell has not yet been written, None is returned.
unsafe { &*self.0.get() }.as_ref()
}
/// Get a reference to the contained value, initializing it if needed using the provided
/// closure.
///
/// Note that:
/// 1) reentrant initialization can cause a stack overflow.
/// 2) if f() temporarily releases the GIL (e.g. by calling `Python::import`) then it is
/// possible (and well-defined) that a second thread may also call get_or_init and begin
/// calling `f()`. Even when this happens `GILOnceCell` guarantees that only **one** write
/// to the cell ever occurs - other threads will simply discard the value they compute and
/// return the result of the first complete computation.
pub fn get_or_init<F>(&self, py: Python, f: F) -> &T
where
F: FnOnce() -> T,
{
let inner = unsafe { &*self.0.get() }.as_ref();
if let Some(value) = inner {
return value;
}
// Note that f() could temporarily release the GIL, so it's possible that another thread
// writes to this GILOnceCell before f() finishes. That's fine; we'll just have to discard
// the value computed here and accept a bit of wasted computation.
let value = f();
let _ = self.set(py, value);
self.get(py).unwrap()
}
/// Get the contents of the cell mutably. This is only possible if the reference to the cell is
/// unique.
pub fn get_mut(&mut self) -> Option<&mut T> {
// Safe because we have &mut self
unsafe { &mut *self.0.get() }.as_mut()
}
/// Set the value in the cell.
///
/// If the cell has already been written, `Err(value)` will be returned containing the new
/// value which was not written.
pub fn set(&self, _py: Python, value: T) -> Result<(), T> {
// Safe because GIL is held, so no other thread can be writing to this cell concurrently.
let inner = unsafe { &mut *self.0.get() };
if inner.is_some() {
return Err(value);
}
*inner = Some(value);
Ok(())
}
}

14
src/pyclass.rs
View File

@ -11,11 +11,11 @@ use std::os::raw::c_void;
use std::ptr;
#[inline]
pub(crate) unsafe fn default_alloc<T: PyTypeInfo>() -> *mut ffi::PyObject {
let type_obj = T::type_object();
pub(crate) unsafe fn default_alloc<T: PyTypeInfo>(py: Python) -> *mut ffi::PyObject {
let type_obj = T::type_object_raw(py);
// if the class derives native types(e.g., PyDict), call special new
if T::FLAGS & type_flags::EXTENDED != 0 && T::BaseLayout::IS_NATIVE_TYPE {
let base_tp = <T::BaseType as PyTypeInfo>::type_object();
let base_tp = T::BaseType::type_object_raw(py);
if let Some(base_new) = base_tp.tp_new {
return base_new(type_obj as *const _ as _, ptr::null_mut(), ptr::null_mut());
}
@ -30,8 +30,8 @@ pub trait PyClassAlloc: PyTypeInfo + Sized {
///
/// # Safety
/// This function must return a valid pointer to the Python heap.
unsafe fn alloc(_py: Python) -> *mut Self::Layout {
default_alloc::<Self>() as _
unsafe fn alloc(py: Python) -> *mut Self::Layout {
default_alloc::<Self>(py) as _
}
/// Deallocate `#[pyclass]` on the Python heap.
@ -45,7 +45,7 @@ pub trait PyClassAlloc: PyTypeInfo + Sized {
return;
}
match Self::type_object().tp_free {
match Self::type_object_raw(py).tp_free {
Some(free) => free(obj as *mut c_void),
None => tp_free_fallback(obj),
}
@ -107,7 +107,7 @@ where
s => CString::new(s)?.into_raw(),
};
type_object.tp_base = <T::BaseType as PyTypeInfo>::type_object() as *const _ as _;
type_object.tp_base = T::BaseType::type_object_raw(py) as *const _ as _;
type_object.tp_name = match module_name {
Some(module_name) => CString::new(format!("{}.{}", module_name, T::NAME))?.into_raw(),

118
src/type_object.rs
View File

@ -1,13 +1,13 @@
// Copyright (c) 2017-present PyO3 Project and Contributors
//! Python type object information
use crate::once_cell::GILOnceCell;
use crate::pyclass::{initialize_type_object, PyClass};
use crate::pyclass_init::PyObjectInit;
use crate::types::{PyAny, PyType};
use crate::{ffi, AsPyPointer, Python};
use std::cell::UnsafeCell;
use std::ptr::NonNull;
use std::sync::atomic::{AtomicBool, Ordering};
use crate::{ffi, AsPyPointer, PyNativeType, Python};
use parking_lot::{const_mutex, Mutex};
use std::thread::{self, ThreadId};
/// `T: PyLayout<U>` represents that `T` is a concrete representaion of `U` in Python heap.
/// E.g., `PyCell` is a concrete representaion of all `pyclass`es, and `ffi::PyObject`
@ -101,18 +101,21 @@ pub unsafe trait PyTypeInfo: Sized {
type AsRefTarget: crate::PyNativeType;
/// PyTypeObject instance for this type.
fn type_object() -> &'static ffi::PyTypeObject;
fn type_object_raw(py: Python) -> &'static ffi::PyTypeObject;
/// Check if `*mut ffi::PyObject` is instance of this type
fn is_instance(object: &PyAny) -> bool {
unsafe {
ffi::PyObject_TypeCheck(object.as_ptr(), Self::type_object() as *const _ as _) != 0
ffi::PyObject_TypeCheck(
object.as_ptr(),
Self::type_object(object.py()) as *const _ as _,
) != 0
}
}
/// Check if `*mut ffi::PyObject` is exact instance of this type
fn is_exact_instance(object: &PyAny) -> bool {
unsafe { (*object.as_ptr()).ob_type == Self::type_object() as *const _ as _ }
unsafe { (*object.as_ptr()).ob_type == Self::type_object(object.py()) as *const _ as _ }
}
}
@ -132,78 +135,63 @@ where
T: PyTypeInfo,
{
fn type_object(py: Python) -> &PyType {
unsafe { py.from_borrowed_ptr(<Self as PyTypeInfo>::type_object() as *const _ as _) }
unsafe { py.from_borrowed_ptr(Self::type_object_raw(py) as *const _ as _) }
}
}
/// Lazy type object for Exceptions
#[doc(hidden)]
pub struct LazyHeapType {
value: UnsafeCell<Option<NonNull<ffi::PyTypeObject>>>,
initialized: AtomicBool,
}
impl LazyHeapType {
pub const fn new() -> Self {
LazyHeapType {
value: UnsafeCell::new(None),
initialized: AtomicBool::new(false),
}
}
pub fn get_or_init<F>(&self, constructor: F) -> NonNull<ffi::PyTypeObject>
where
F: Fn(Python) -> NonNull<ffi::PyTypeObject>,
{
if !self
.initialized
.compare_and_swap(false, true, Ordering::Acquire)
{
// We have to get the GIL before setting the value to the global!!!
let gil = Python::acquire_gil();
unsafe {
*self.value.get() = Some(constructor(gil.python()));
}
}
unsafe { (*self.value.get()).unwrap() }
}
}
// This is necessary for making static `LazyHeapType`s
//
// Type objects are shared between threads by the Python interpreter anyway, so it is no worse
// to allow sharing on the Rust side too.
unsafe impl Sync for LazyHeapType {}
/// Lazy type object for PyClass
#[doc(hidden)]
pub struct LazyStaticType {
value: UnsafeCell<ffi::PyTypeObject>,
initialized: AtomicBool,
// Boxed because Python expects the type object to have a stable address.
value: GILOnceCell<Box<ffi::PyTypeObject>>,
// Threads which have begun initialization. Used for reentrant initialization detection.
initializing_threads: Mutex<Vec<ThreadId>>,
}
impl LazyStaticType {
pub const fn new() -> Self {
LazyStaticType {
value: UnsafeCell::new(ffi::PyTypeObject_INIT),
initialized: AtomicBool::new(false),
value: GILOnceCell::new(),
initializing_threads: const_mutex(Vec::new()),
}
}
pub fn get_or_init<T: PyClass>(&self) -> &ffi::PyTypeObject {
if !self
.initialized
.compare_and_swap(false, true, Ordering::Acquire)
{
let gil = Python::acquire_gil();
let py = gil.python();
initialize_type_object::<T>(py, T::MODULE, unsafe { &mut *self.value.get() })
.unwrap_or_else(|e| {
e.print(py);
panic!("An error occurred while initializing class {}", T::NAME)
});
}
unsafe { &*self.value.get() }
pub fn get_or_init<T: PyClass>(&self, py: Python) -> &ffi::PyTypeObject {
self.value
.get_or_init(py, || {
{
// Code evaluated at class init time, such as class attributes, might lead to
// recursive initalization of the type object if the class attribute is the same
// type as the class.
//
// That could lead to all sorts of unsafety such as using incomplete type objects
// to initialize class instances, so recursive initialization is prevented.
let thread_id = thread::current().id();
let mut threads = self.initializing_threads.lock();
if threads.contains(&thread_id) {
panic!("Recursive initialization of type_object for {}", T::NAME);
} else {
threads.push(thread_id)
}
}
// Okay, not recursive initialization - can proceed safely.
let mut type_object = Box::new(ffi::PyTypeObject_INIT);
initialize_type_object::<T>(py, T::MODULE, type_object.as_mut()).unwrap_or_else(
|e| {
e.print(py);
panic!("An error occurred while initializing class {}", T::NAME)
},
);
// Initialization successfully complete, can clear the thread list.
// (No futher calls to get_or_init() will try to init, on any thread.)
*self.initializing_threads.lock() = Vec::new();
type_object
})
.as_ref()
}
}

2
src/types/mod.rs
View File

@ -143,7 +143,7 @@ macro_rules! pyobject_native_type_convert(
const MODULE: Option<&'static str> = $module;
#[inline]
fn type_object() -> &'static $crate::ffi::PyTypeObject {
fn type_object_raw(_py: Python) -> &'static $crate::ffi::PyTypeObject {
unsafe{ &$typeobject }
}

33
tests/test_class_attributes.rs
View File

@ -30,25 +30,12 @@ impl Foo {
"bar".to_string()
}
#[classattr]
fn foo() -> Foo {
Foo { x: 1 }
}
#[classattr]
fn bar() -> Bar {
Bar { x: 2 }
}
}
#[pymethods]
impl Bar {
#[classattr]
fn foo() -> Foo {
Foo { x: 3 }
}
}
#[test]
fn class_attributes() {
let gil = Python::acquire_gil();
@ -67,13 +54,23 @@ fn class_attributes_are_immutable() {
py_expect_exception!(py, foo_obj, "foo_obj.a = 6", TypeError);
}
#[pyclass]
struct SelfClassAttribute {
#[pyo3(get)]
x: i32,
}
#[pymethods]
impl SelfClassAttribute {
#[classattr]
const SELF: SelfClassAttribute = SelfClassAttribute { x: 1 };
}
#[test]
#[should_panic(expected = "Recursive initialization of type_object for SelfClassAttribute")]
fn recursive_class_attributes() {
let gil = Python::acquire_gil();
let py = gil.python();
let foo_obj = py.get_type::<Foo>();
let bar_obj = py.get_type::<Bar>();
py_assert!(py, foo_obj, "foo_obj.foo.x == 1");
py_assert!(py, foo_obj, "foo_obj.bar.x == 2");
py_assert!(py, bar_obj, "bar_obj.foo.x == 3");
py.get_type::<SelfClassAttribute>();
}