From 33617bfffc6187aa7f57e56bd21800fa52b387eb Mon Sep 17 00:00:00 2001
From: David <1939362+davidhewitt@users.noreply.github.com>
Date: Sun, 31 May 2020 16:15:33 +0100
Subject: [PATCH] Require Send for #[pyclass]

---
 CHANGELOG.md               |  1 +
 guide/src/class.md         |  5 ++---
 src/pyclass.rs             |  4 +++-
 tests/test_gc.rs           | 11 +++++------
 tests/ui/static_ref.rs     | 14 +++-----------
 tests/ui/static_ref.stderr |  6 +++---
 6 files changed, 17 insertions(+), 24 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 53020074e40..52b31d41721 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Simplify internals of `#[pyo3(get)]` attribute. (Remove the hidden API `GetPropertyValue`.) [#934](https://github.com/PyO3/pyo3/pull/934)
 - Call `Py_Finalize` at exit to flush buffers, etc. [#943](https://github.com/PyO3/pyo3/pull/943)
 - Add type parameter to PyBuffer. #[951](https://github.com/PyO3/pyo3/pull/951)
+- Require `Send` bound for `#[pyclass]`. [#966](https://github.com/PyO3/pyo3/pull/966)
 
 ### Removed
 - Remove `ManagedPyRef` (unused, and needs specialization) [#930](https://github.com/PyO3/pyo3/pull/930)
diff --git a/guide/src/class.md b/guide/src/class.md
index a8990556e65..95c9f1877c8 100644
--- a/guide/src/class.md
+++ b/guide/src/class.md
@@ -14,10 +14,9 @@ struct MyClass {
 }
 ```
 
-The above example generates implementations for [`PyTypeInfo`], [`PyTypeObject`],
-and [`PyClass`] for `MyClass`.
+Because Python objects are freely shared between threads by the Python interpreter, all structs annotated with `#[pyclass]` must implement `Send`.
 
-If you curious what `#[pyclass]` generates, see [How methods are implemented](#how-methods-are-implemented) section.
+The above example generates implementations for [`PyTypeInfo`], [`PyTypeObject`], and [`PyClass`] for `MyClass`. To see these generated implementations, refer to the section [How methods are implemented](#how-methods-are-implemented) at the end of this chapter.
 
 ## Adding the class to a module
 
diff --git a/src/pyclass.rs b/src/pyclass.rs
index 5e0b05e3ae8..9d7bc8def10 100644
--- a/src/pyclass.rs
+++ b/src/pyclass.rs
@@ -72,7 +72,9 @@ pub unsafe fn tp_free_fallback(obj: *mut ffi::PyObject) {
 ///
 /// The `#[pyclass]` attribute automatically implements this trait for your Rust struct,
 /// so you don't have to use this trait directly.
-pub trait PyClass: PyTypeInfo<Layout = PyCell<Self>> + Sized + PyClassAlloc + PyMethods {
+pub trait PyClass:
+    PyTypeInfo<Layout = PyCell<Self>> + Sized + PyClassAlloc + PyMethods + Send
+{
     /// Specify this class has `#[pyclass(dict)]` or not.
     type Dict: PyClassDict;
     /// Specify this class has `#[pyclass(weakref)]` or not.
diff --git a/tests/test_gc.rs b/tests/test_gc.rs
index 0b01de83211..ba63b2a57b4 100644
--- a/tests/test_gc.rs
+++ b/tests/test_gc.rs
@@ -4,7 +4,6 @@ use pyo3::class::PyVisit;
 use pyo3::prelude::*;
 use pyo3::type_object::PyTypeObject;
 use pyo3::{py_run, AsPyPointer, PyCell, PyTryInto};
-use std::cell::RefCell;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 
@@ -84,19 +83,19 @@ fn data_is_dropped() {
 #[allow(dead_code)]
 #[pyclass]
 struct GCIntegration {
-    self_ref: RefCell<PyObject>,
+    self_ref: PyObject,
     dropped: TestDropCall,
 }
 
 #[pyproto]
 impl PyGCProtocol for GCIntegration {
     fn __traverse__(&self, visit: PyVisit) -> Result<(), PyTraverseError> {
-        visit.call(&*self.self_ref.borrow())
+        visit.call(&self.self_ref)
     }
 
     fn __clear__(&mut self) {
         let gil = GILGuard::acquire();
-        *self.self_ref.borrow_mut() = gil.python().None();
+        self.self_ref = gil.python().None();
     }
 }
 
@@ -110,7 +109,7 @@ fn gc_integration() {
         let inst = PyCell::new(
             py,
             GCIntegration {
-                self_ref: RefCell::new(py.None()),
+                self_ref: py.None(),
                 dropped: TestDropCall {
                     drop_called: Arc::clone(&drop_called),
                 },
@@ -119,7 +118,7 @@ fn gc_integration() {
         .unwrap();
 
         let mut borrow = inst.borrow_mut();
-        *borrow.self_ref.borrow_mut() = inst.to_object(py);
+        borrow.self_ref = inst.to_object(py);
     }
 
     let gil = Python::acquire_gil();
diff --git a/tests/ui/static_ref.rs b/tests/ui/static_ref.rs
index 5202920ac03..a426536d499 100644
--- a/tests/ui/static_ref.rs
+++ b/tests/ui/static_ref.rs
@@ -1,17 +1,9 @@
 use pyo3::prelude::*;
 use pyo3::types::PyList;
 
-#[pyclass]
-struct MyClass {
-    list: &'static PyList,
-}
-
-#[pymethods]
-impl MyClass {
-    #[new]
-    fn new(list: &'static PyList) -> Self {
-        Self { list }
-    }
+#[pyfunction]
+fn static_ref(list: &'static PyList) -> usize {
+    list.len()
 }
 
 fn main() {}
diff --git a/tests/ui/static_ref.stderr b/tests/ui/static_ref.stderr
index a708fdeab3b..1e093a35a29 100644
--- a/tests/ui/static_ref.stderr
+++ b/tests/ui/static_ref.stderr
@@ -1,8 +1,8 @@
 error[E0597]: `pool` does not live long enough
- --> $DIR/static_ref.rs:9:1
+ --> $DIR/static_ref.rs:4:1
   |
-9 | #[pymethods]
-  | ^^^^^^^^^^^^
+4 | #[pyfunction]
+  | ^^^^^^^^^^^^^
   | |
   | borrowed value does not live long enough
   | `pool` dropped here while still borrowed