Opt out of PyCell borrow tracking

guide/src/class.md

@@ -78,7 +78,7 @@ For users who are not very familiar with `RefCell`, here is a reminder of Rust's
 
 ```rust
 # use pyo3::prelude::*;
-#[pyclass]
+#[pyclass(mutable)]
 struct MyClass {
     #[pyo3(get)]
     num: i32,
@@ -299,7 +299,7 @@ use pyo3::types::PyDict;
 use pyo3::AsPyPointer;
 use std::collections::HashMap;
 
-#[pyclass(extends=PyDict)]
+#[pyclass(extends=PyDict, mutable)]
 #[derive(Default)]
 struct DictWithCounter {
     counter: HashMap<String, usize>,
@@ -362,7 +362,7 @@ For simple cases where a member variable is just read and written with no side e
 
 ```rust
 # use pyo3::prelude::*;
-#[pyclass]
+#[pyclass(mutable)]
 struct MyClass {
     #[pyo3(get, set)]
     num: i32
@@ -410,7 +410,7 @@ can be used since Rust 2018).
 
 ```rust
 # use pyo3::prelude::*;
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct MyClass {
 #     num: i32,
 # }
@@ -436,7 +436,7 @@ If this parameter is specified, it is used as the property name, i.e.
 
 ```rust
 # use pyo3::prelude::*;
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct MyClass {
 #    num: i32,
 # }
@@ -473,7 +473,7 @@ between those accessible to Python (and Rust) and those accessible only to Rust.
 
 ```rust
 # use pyo3::prelude::*;
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct MyClass {
 #     num: i32,
 # }
@@ -641,7 +641,7 @@ Example:
 # use pyo3::prelude::*;
 use pyo3::types::{PyDict, PyTuple};
 #
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct MyClass {
 #     num: i32,
 # }
@@ -731,7 +731,7 @@ unsafe impl pyo3::PyTypeInfo for MyClass {
     }
 }
 
-impl pyo3::pyclass::PyClass for MyClass {
+unsafe impl pyo3::pyclass::PyClass for MyClass {
     type Dict = pyo3::pyclass_slots::PyClassDummySlot;
     type WeakRef = pyo3::pyclass_slots::PyClassDummySlot;
     type BaseNativeType = PyAny;

guide/src/class/protocols.md

@@ -67,7 +67,7 @@ as argument and calls that object when called.
 # use pyo3::prelude::*;
 # use pyo3::types::{PyDict, PyTuple};
 #
-#[pyclass(name = "counter")]
+#[pyclass(name = "counter", mutable)]
 struct PyCounter {
     count: u64,
     wraps: Py<PyAny>,
@@ -453,7 +453,7 @@ use pyo3::prelude::*;
 use pyo3::PyTraverseError;
 use pyo3::gc::{PyGCProtocol, PyVisit};
 
-#[pyclass]
+#[pyclass(mutable)]
 struct ClassWithGCSupport {
     obj: Option<PyObject>,
 }
@@ -505,7 +505,7 @@ Example:
 use pyo3::prelude::*;
 use pyo3::PyIterProtocol;
 
-#[pyclass]
+#[pyclass(mutable)]
 struct MyIterator {
     iter: Box<dyn Iterator<Item = PyObject> + Send>,
 }
@@ -530,7 +530,7 @@ implementations in `PyIterProtocol` will ensure that the objects behave correctl
 # use pyo3::prelude::*;
 # use pyo3::PyIterProtocol;
 
-#[pyclass]
+#[pyclass(mutable)]
 struct Iter {
     inner: std::vec::IntoIter<usize>,
 }

guide/src/migration.md

@@ -436,7 +436,7 @@ Here is an example.
 ```rust
 # use pyo3::prelude::*;
 
-#[pyclass]
+#[pyclass(mutable)]
 struct Names {
     names: Vec<String>
 }
@@ -514,7 +514,7 @@ After:
 ```rust
 # use pyo3::prelude::*;
 # use pyo3::types::IntoPyDict;
-# #[pyclass] #[derive(Clone)] struct MyClass {}
+# #[pyclass(mutable)] #[derive(Clone)] struct MyClass {}
 # #[pymethods] impl MyClass { #[new]fn new() -> Self { MyClass {} }}
 # Python::with_gil(|py| {
 # let typeobj = py.get_type::<MyClass>();

guide/src/trait_bounds.md

@@ -127,7 +127,7 @@ Let's add the PyO3 annotations and add a constructor:
 # use pyo3::prelude::*;
 # use pyo3::types::PyAny;
 
-#[pyclass]
+#[pyclass(mutable)]
 struct UserModel {
     model: Py<PyAny>,
 }
@@ -173,7 +173,7 @@ This wrapper will also perform the type conversions between Python and Rust.
 #   fn get_results(&self) -> Vec<f64>;
 # }
 #
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct UserModel {
 #     model: Py<PyAny>,
 # }
@@ -342,7 +342,7 @@ We used in our `get_results` method the following call that performs the type co
 #   fn get_results(&self) -> Vec<f64>;
 # }
 #
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct UserModel {
 #     model: Py<PyAny>,
 # }
@@ -395,7 +395,7 @@ Let's break it down in order to perform better error handling:
 #   fn get_results(&self) -> Vec<f64>;
 # }
 #
-# #[pyclass]
+# #[pyclass(mutable)]
 # struct UserModel {
 #     model: Py<PyAny>,
 # }
@@ -481,7 +481,7 @@ pub fn solve_wrapper(model: &mut UserModel) {
     solve(model);
 }
 
-#[pyclass]
+#[pyclass(mutable)]
 pub struct UserModel {
     model: Py<PyAny>,
 }

guide/src/types.md

@@ -87,7 +87,7 @@ For a `&PyAny` object reference `any` where the underlying object is a `#[pyclas
 ```rust
 # use pyo3::prelude::*;
 # use pyo3::{Py, Python, PyAny, PyResult};
-# #[pyclass] #[derive(Clone)] struct MyClass { }
+# #[pyclass(mutable)] #[derive(Clone)] struct MyClass { }
 # Python::with_gil(|py| -> PyResult<()> {
 let obj: &PyAny = Py::new(py, MyClass { })?.into_ref(py);
 
@@ -191,7 +191,7 @@ For a `#[pyclass] struct MyClass`, the conversions for `Py<MyClass>` are below:
 ```rust
 # use pyo3::prelude::*;
 # Python::with_gil(|py| {
-# #[pyclass] struct MyClass { }
+# #[pyclass(mutable)] struct MyClass { }
 # Python::with_gil(|py| -> PyResult<()> {
 let my_class: Py<MyClass> = Py::new(py, MyClass { })?;
 
@@ -236,7 +236,7 @@ so it also exposes all of the methods on `PyAny`.
 
 ```rust
 # use pyo3::prelude::*;
-# #[pyclass] struct MyClass { }
+# #[pyclass(mutable)] struct MyClass { }
 # Python::with_gil(|py| -> PyResult<()> {
 let cell: &PyCell<MyClass> = PyCell::new(py, MyClass { })?;
 

pyo3-macros-backend/src/pyclass.rs

@@ -26,6 +26,7 @@ pub struct PyClassArgs {
     pub is_basetype: bool,
     pub has_extends: bool,
     pub has_unsendable: bool,
+    pub is_mutable: bool,
     pub module: Option<syn::LitStr>,
 }
 
@@ -54,6 +55,7 @@ impl Default for PyClassArgs {
             is_basetype: false,
             has_extends: false,
             has_unsendable: false,
+            is_mutable: false,
         }
     }
 }
@@ -158,6 +160,9 @@ impl PyClassArgs {
             "unsendable" => {
                 self.has_unsendable = true;
             }
+            "mutable" => {
+                self.is_mutable = true;
+            }
             _ => bail_spanned!(
                 exp.path.span() => "expected one of gc/weakref/subclass/dict/unsendable"
             ),
@@ -515,6 +520,52 @@ fn impl_class(
     let is_basetype = attr.is_basetype;
     let is_subclass = attr.has_extends;
 
+    // If the pyclass has extends/unsendable, we must opt back into PyCell checking
+    // so that the inner Rust object is not inappropriately shared between threads.
+    let impl_pyclass = if attr.has_unsendable || attr.has_extends || attr.is_mutable {
+        quote! {
+            unsafe impl ::pyo3::pyclass::MutablePyClass for #cls {}
+
+            unsafe impl ::pyo3::PyClass for #cls {
+                type Dict = #dict;
+                type WeakRef = #weakref;
+                type BaseNativeType = #base_nativetype;
+
+                #[inline]
+                fn try_borrow_as_pyref(slf: &::pyo3::PyCell<Self>) -> ::std::result::Result<::pyo3::pycell::PyRef<'_, Self>, ::pyo3::pycell::PyBorrowError> {
+                    unsafe { ::pyo3::PyCell::immutable_pyclass_try_borrow(slf) }
+                }
+
+                #[inline]
+                fn borrow_as_pyref(slf: &::pyo3::PyCell<Self>) -> ::pyo3::pycell::PyRef<'_, Self> {
+                    unsafe { ::pyo3::PyCell::immutable_pyclass_borrow(slf) }
+                }
+
+                #[inline]
+                unsafe fn try_borrow_unguarded(slf: &::pyo3::PyCell<Self>) -> ::std::result::Result<&Self, ::pyo3::pycell::PyBorrowError> {
+                    ::pyo3::PyCell::immutable_pyclass_try_borrow_unguarded(slf)
+                }
+
+                #[inline]
+                unsafe fn drop_pyref(pyref: &mut ::pyo3::pycell::PyRef<Self>) {
+                    ::pyo3::pycell::PyRef::decrement_flag(pyref)
+                }
+            }
+
+            impl<'a> ::pyo3::derive_utils::ExtractExt<'a> for &'a mut #cls {
+                type Target = ::pyo3::PyRefMut<'a, #cls>;
+            }
+        }
+    } else {
+        quote! {
+            unsafe impl ::pyo3::PyClass for #cls {
+                type Dict = #dict;
+                type WeakRef = #weakref;
+                type BaseNativeType = #base_nativetype;
+            }
+        }
+    };
+
     Ok(quote! {
         unsafe impl ::pyo3::type_object::PyTypeInfo for #cls {
             type AsRefTarget = ::pyo3::PyCell<Self>;
@@ -532,21 +583,14 @@ fn impl_class(
             }
         }
 
-        impl ::pyo3::PyClass for #cls {
-            type Dict = #dict;
-            type WeakRef = #weakref;
-            type BaseNativeType = #base_nativetype;
-        }
+        #impl_pyclass
 
         impl<'a> ::pyo3::derive_utils::ExtractExt<'a> for &'a #cls
         {
             type Target = ::pyo3::PyRef<'a, #cls>;
         }
 
-        impl<'a> ::pyo3::derive_utils::ExtractExt<'a> for &'a mut #cls
-        {
-            type Target = ::pyo3::PyRefMut<'a, #cls>;
-        }
+
 
         #into_pyobject
 

src/class/basic.rs

@@ -9,6 +9,7 @@
 //! [typeobj docs](https://docs.python.org/3/c-api/typeobj.html)
 
 use crate::callback::{HashCallbackOutput, IntoPyCallbackOutput};
+use crate::pyclass::MutablePyClass;
 use crate::{exceptions, ffi, FromPyObject, PyAny, PyCell, PyClass, PyObject};
 use std::os::raw::c_int;
 
@@ -128,12 +129,12 @@ pub trait PyObjectGetAttrProtocol<'p>: PyObjectProtocol<'p> {
     type Name: FromPyObject<'p>;
     type Result: IntoPyCallbackOutput<PyObject>;
 }
-pub trait PyObjectSetAttrProtocol<'p>: PyObjectProtocol<'p> {
+pub trait PyObjectSetAttrProtocol<'p>: PyObjectProtocol<'p> + MutablePyClass {
     type Name: FromPyObject<'p>;
     type Value: FromPyObject<'p>;
     type Result: IntoPyCallbackOutput<()>;
 }
-pub trait PyObjectDelAttrProtocol<'p>: PyObjectProtocol<'p> {
+pub trait PyObjectDelAttrProtocol<'p>: PyObjectProtocol<'p> + MutablePyClass {
     type Name: FromPyObject<'p>;
     type Result: IntoPyCallbackOutput<()>;
 }

src/class/buffer.rs

@@ -5,15 +5,16 @@
 //! For more information check [buffer protocol](https://docs.python.org/3/c-api/buffer.html)
 //! c-api
 use crate::callback::IntoPyCallbackOutput;
-use crate::{ffi, PyCell, PyClass, PyRefMut};
+use crate::pyclass::MutablePyClass;
+use crate::{ffi, PyCell, PyRefMut};
 use std::os::raw::c_int;
 
 /// Buffer protocol interface
 ///
 /// For more information check [buffer protocol](https://docs.python.org/3/c-api/buffer.html)
 /// c-api.
 #[allow(unused_variables)]
-pub trait PyBufferProtocol<'p>: PyClass {
+pub trait PyBufferProtocol<'p>: MutablePyClass {
     // No default implementations so that implementors of this trait provide both methods.
 
     fn bf_getbuffer(slf: PyRefMut<Self>, view: *mut ffi::Py_buffer, flags: c_int) -> Self::Result
@@ -51,7 +52,7 @@ where
 #[doc(hidden)]
 pub unsafe extern "C" fn releasebuffer<T>(slf: *mut ffi::PyObject, arg1: *mut ffi::Py_buffer)
 where
-    T: for<'p> PyBufferReleaseBufferProtocol<'p>,
+    T: for<'p> PyBufferReleaseBufferProtocol<'p> + MutablePyClass,
 {
     crate::callback_body!(py, {
         let slf = py.from_borrowed_ptr::<crate::PyCell<T>>(slf);

src/class/gc.rs

@@ -2,6 +2,7 @@
 
 //! Python GC support
 
+use crate::pyclass::MutablePyClass;
 use crate::{ffi, AsPyPointer, PyCell, PyClass, Python};
 use std::os::raw::{c_int, c_void};
 
@@ -53,7 +54,7 @@ where
 #[doc(hidden)]
 pub unsafe extern "C" fn clear<T>(slf: *mut ffi::PyObject) -> c_int
 where
-    T: for<'p> PyGCClearProtocol<'p>,
+    T: for<'p> PyGCClearProtocol<'p> + MutablePyClass,
 {
     let pool = crate::GILPool::new();
     let slf = pool.python().from_borrowed_ptr::<PyCell<T>>(slf);

src/class/iter.rs

@@ -21,7 +21,7 @@ use crate::{ffi, IntoPy, IntoPyPointer, PyClass, PyObject, Python};
 /// use pyo3::prelude::*;
 /// use pyo3::PyIterProtocol;
 ///
-/// #[pyclass]
+/// #[pyclass(mutable)]
 /// struct Iter {
 ///     count: usize,
 /// }