# HG changeset patch
# User Yuya Nishihara <yuya@tcha.org>
# Date 2019-09-16 22:59:25
# Node ID a1908eb08342402ed2ca79a351c0333612bf2237
# Parent  1c675c5fe5fe88b248c05b6c2f039f59320147fc

rust-cpython: mark PySharedState as Sync so &'PySharedState can be Send

The goal is to store &'static PySharedState in $leaked struct, which allows
us to move the $leaked struct out of the macro. Currently, it depends on
inner.$data_member(py), which can't be generalized.

PySharedState is Sync because any mutation or read operation is synchronized
by the Python GIL, py: Python<'a>, which should guarantee that &'PySharedState
can be sent to another thread.

diff --git a/rust/hg-cpython/src/ref_sharing.rs b/rust/hg-cpython/src/ref_sharing.rs
--- a/rust/hg-cpython/src/ref_sharing.rs
+++ b/rust/hg-cpython/src/ref_sharing.rs
@@ -33,6 +33,10 @@ pub struct PySharedState {
     mutably_borrowed: Cell<bool>,
 }
 
+// &PySharedState can be Send because any access to inner cells is
+// synchronized by the GIL.
+unsafe impl Sync for PySharedState {}
+
 impl PySharedState {
     pub fn borrow_mut<'a, T>(
         &'a self,