feat: allow async methods to accept &self/&mut self

Author: wyfo

guide/src/async-await.md

@@ -30,8 +30,7 @@ Resulting future of an `async fn` decorated by `#[pyfunction]` must be `Send + '
 
 As a consequence, `async fn` parameters and return types must also be `Send + 'static`, so it is not possible to have a signature like `async fn does_not_compile(arg: &PyAny, py: Python<'_>) -> &PyAny`.
 
-It also means that methods cannot use `&self`/`&mut self`, *but this restriction should be dropped in the future.*
-
+However, there is an exception for method receiver, so async methods can accept `&self`/`&mut self`
 
 ## Implicit GIL holding
 

newsfragments/3609.changed.md

@@ -0,0 +1 @@
+Allow async methods to accept `&self`/`&mut self`

pyo3-macros-backend/src/method.rs

@@ -1,18 +1,19 @@
 use std::fmt::Display;
 
-use crate::attributes::{TextSignatureAttribute, TextSignatureAttributeValue};
-use crate::deprecations::{Deprecation, Deprecations};
-use crate::params::impl_arg_params;
-use crate::pyfunction::{FunctionSignature, PyFunctionArgPyO3Attributes};
-use crate::pyfunction::{PyFunctionOptions, SignatureAttribute};
-use crate::quotes;
-use crate::utils::{self, PythonDoc};
 use proc_macro2::{Span, TokenStream};
-use quote::ToTokens;
-use quote::{quote, quote_spanned};
-use syn::ext::IdentExt;
-use syn::spanned::Spanned;
-use syn::{Ident, Result};
+use quote::{quote, quote_spanned, ToTokens};
+use syn::{ext::IdentExt, spanned::Spanned, Ident, Result};
+
+use crate::{
+    attributes::{TextSignatureAttribute, TextSignatureAttributeValue},
+    deprecations::{Deprecation, Deprecations},
+    params::impl_arg_params,
+    pyfunction::{
+        FunctionSignature, PyFunctionArgPyO3Attributes, PyFunctionOptions, SignatureAttribute,
+    },
+    quotes,
+    utils::{self, PythonDoc},
+};
 
 #[derive(Clone, Debug)]
 pub struct FnArg<'a> {
@@ -473,8 +474,7 @@ impl<'a> FnSpec<'a> {
         }
 
         let rust_call = |args: Vec<TokenStream>| {
-            let mut call = quote! { function(#self_arg #(#args),*) };
-            if self.asyncness.is_some() {
+            let call = if self.asyncness.is_some() {
                 let throw_callback = if cancel_handle.is_some() {
                     quote! { Some(__throw_callback) }
                 } else {
@@ -485,8 +485,19 @@ impl<'a> FnSpec<'a> {
                     Some(cls) => quote!(Some(<#cls as _pyo3::PyTypeInfo>::NAME)),
                     None => quote!(None),
                 };
-                call = quote! {{
-                    let future = #call;
+                let future = match self.tp {
+                    FnType::Fn(SelfType::Receiver { mutable: false, .. }) => quote! {{
+                        let __guard = _pyo3::impl_::coroutine::RefGuard::<#cls>::new(py.from_borrowed_ptr::<_pyo3::types::PyAny>(_slf))?;
+                        async move { function(&__guard, #(#args),*).await }
+                    }},
+                    FnType::Fn(SelfType::Receiver { mutable: true, .. }) => quote! {{
+                        let mut __guard = _pyo3::impl_::coroutine::RefMutGuard::<#cls>::new(py.from_borrowed_ptr::<_pyo3::types::PyAny>(_slf))?;
+                        async move { function(&mut __guard, #(#args),*).await }
+                    }},
+                    _ => quote! { function(#self_arg #(#args),*) },
+                };
+                let mut call = quote! {{
+                    let future = #future;
                     _pyo3::impl_::coroutine::new_coroutine(
                         _pyo3::intern!(py, stringify!(#python_name)),
                         #qualname_prefix,
@@ -501,7 +512,10 @@ impl<'a> FnSpec<'a> {
                         #call
                     }};
                 }
-            }
+                call
+            } else {
+                quote! { function(#self_arg #(#args),*) }
+            };
             quotes::map_result_into_ptr(quotes::ok_wrap(call))
         };
 

src/impl_/coroutine.rs

@@ -1,7 +1,15 @@
-use std::future::Future;
+use std::{
+    future::Future,
+    mem,
+    ops::{Deref, DerefMut},
+};
 
-use crate::coroutine::cancel::ThrowCallback;
-use crate::{coroutine::Coroutine, types::PyString, IntoPy, PyErr, PyObject};
+use crate::{
+    coroutine::{cancel::ThrowCallback, Coroutine},
+    pyclass::boolean_struct::False,
+    types::PyString,
+    IntoPy, Py, PyAny, PyCell, PyClass, PyErr, PyObject, PyResult, Python,
+};
 
 pub fn new_coroutine<F, T, E>(
     name: &PyString,
@@ -16,3 +24,63 @@ where
 {
     Coroutine::new(Some(name.into()), qualname_prefix, throw_callback, future)
 }
+
+fn get_ptr<T: PyClass>(obj: &Py<T>) -> *mut T {
+    // SAFETY: Py<T> can be casted as *const PyCell<T>
+    unsafe { &*(obj.as_ptr() as *const PyCell<T>) }.get_ptr()
+}
+
+pub struct RefGuard<T: PyClass>(Py<T>);
+
+impl<T: PyClass> RefGuard<T> {
+    pub fn new(obj: &PyAny) -> PyResult<Self> {
+        let owned: Py<T> = obj.extract()?;
+        mem::forget(owned.try_borrow(obj.py())?);
+        Ok(RefGuard(owned))
+    }
+}
+
+impl<T: PyClass> Deref for RefGuard<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: `RefGuard` has been built from `PyRef` and provides the same guarantees
+        unsafe { &*get_ptr(&self.0) }
+    }
+}
+
+impl<T: PyClass> Drop for RefGuard<T> {
+    fn drop(&mut self) {
+        Python::with_gil(|gil| self.0.as_ref(gil).release_ref())
+    }
+}
+
+pub struct RefMutGuard<T: PyClass<Frozen = False>>(Py<T>);
+
+impl<T: PyClass<Frozen = False>> RefMutGuard<T> {
+    pub fn new(obj: &PyAny) -> PyResult<Self> {
+        let owned: Py<T> = obj.extract()?;
+        mem::forget(owned.try_borrow_mut(obj.py())?);
+        Ok(RefMutGuard(owned))
+    }
+}
+
+impl<T: PyClass<Frozen = False>> Deref for RefMutGuard<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: `RefMutGuard` has been built from `PyRefMut` and provides the same guarantees
+        unsafe { &*get_ptr(&self.0) }
+    }
+}
+
+impl<T: PyClass<Frozen = False>> DerefMut for RefMutGuard<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: `RefMutGuard` has been built from `PyRefMut` and provides the same guarantees
+        unsafe { &mut *get_ptr(&self.0) }
+    }
+}
+
+impl<T: PyClass<Frozen = False>> Drop for RefMutGuard<T> {
+    fn drop(&mut self) {
+        Python::with_gil(|gil| self.0.as_ref(gil).release_mut())
+    }
+}

src/pycell.rs

@@ -516,6 +516,16 @@ impl<T: PyClass> PyCell<T> {
         #[allow(clippy::useless_conversion)]
         offset.try_into().expect("offset should fit in Py_ssize_t")
     }
+
+    #[cfg(feature = "macros")]
+    pub(crate) fn release_ref(&self) {
+        self.borrow_checker().release_borrow();
+    }
+
+    #[cfg(feature = "macros")]
+    pub(crate) fn release_mut(&self) {
+        self.borrow_checker().release_borrow_mut();
+    }
 }
 
 impl<T: PyClassImpl> PyCell<T> {

tests/test_coroutine.rs

@@ -234,3 +234,56 @@ fn coroutine_panic() {
         py_run!(gil, panic, &handle_windows(test));
     })
 }
+
+#[test]
+fn test_async_method_receiver() {
+    #[pyclass]
+    struct Counter(usize);
+    #[pymethods]
+    impl Counter {
+        #[new]
+        fn new() -> Self {
+            Self(0)
+        }
+        async fn get(&self) -> usize {
+            self.0
+        }
+        async fn incr(&mut self) -> usize {
+            self.0 += 1;
+            self.0
+        }
+    }
+    Python::with_gil(|gil| {
+        let test = r#"
+        import asyncio
+        
+        obj = Counter()
+        coro1 = obj.get()
+        coro2 = obj.get()
+        try:
+            obj.incr()  # borrow checking should fail
+        except RuntimeError as err:
+            pass
+        else:
+            assert False
+        assert asyncio.run(coro1) == 0
+        coro2.close()
+        coro3 = obj.incr()
+        try:
+            obj.incr()  # borrow checking should fail
+        except RuntimeError as err:
+            pass
+        else:
+            assert False
+        try:
+            obj.get() # borrow checking should fail
+        except RuntimeError as err:
+            pass
+        else:
+            assert False
+        assert asyncio.run(coro3) == 1
+        "#;
+        let locals = [("Counter", gil.get_type::<Counter>())].into_py_dict(gil);
+        py_run!(gil, *locals, test);
+    })
+}