Make EventLoopProxy Sync

Co-authored-by: daxpedda <daxpedda@gmail.com>
Closes: #3448

CHANGELOG.md

@@ -14,6 +14,7 @@ Unreleased` header.
 - On X11, don't require XIM to run.
 - On X11, fix xkb state not being updated correctly sometimes leading to wrong input.
 - Fix compatibility with 32-bit platforms without 64-bit atomics.
+- Implement `Sync` for `EventLoopProxy<T: Send>`.
 - On X11, fix swapped instance and general class names.
 - **Breaking:** Removed unnecessary generic parameter `T` from `EventLoopWindowTarget`.
 - On Windows, macOS, X11, Wayland and Web, implement setting images as cursors. See the `custom_cursors.rs` example.

src/event_loop.rs

@@ -253,7 +253,8 @@ impl<T> EventLoop<T> {
         self.event_loop.run(event_handler)
     }
 
-    /// Creates an [`EventLoopProxy`] that can be used to dispatch user events to the main event loop.
+    /// Creates an [`EventLoopProxy`] that can be used to dispatch user events
+    /// to the main event loop, possibly from another thread.
     pub fn create_proxy(&self) -> EventLoopProxy<T> {
         EventLoopProxy {
             event_loop_proxy: self.event_loop.create_proxy(),

src/platform_impl/ios/event_loop.rs

@@ -229,6 +229,7 @@ pub struct EventLoopProxy<T> {
 }
 
 unsafe impl<T: Send> Send for EventLoopProxy<T> {}
+unsafe impl<T: Send> Sync for EventLoopProxy<T> {}
 
 impl<T> Clone for EventLoopProxy<T> {
     fn clone(&self) -> EventLoopProxy<T> {

src/platform_impl/macos/event_loop.rs

@@ -532,6 +532,7 @@ pub struct EventLoopProxy<T> {
 }
 
 unsafe impl<T: Send> Send for EventLoopProxy<T> {}
+unsafe impl<T: Send> Sync for EventLoopProxy<T> {}
 
 impl<T> Drop for EventLoopProxy<T> {
     fn drop(&mut self) {

src/platform_impl/web/async/dispatcher.rs

@@ -5,7 +5,7 @@ use std::{
     sync::{Arc, Condvar, Mutex},
 };
 
-pub struct Dispatcher<T: 'static>(Wrapper<true, T, Sender<Closure<T>>, Closure<T>>);
+pub struct Dispatcher<T: 'static>(Wrapper<T, Sender<Closure<T>>, Closure<T>>);
 
 struct Closure<T>(Box<dyn FnOnce(&T) + Send>);
 
@@ -85,7 +85,7 @@ impl<T> Dispatcher<T> {
 }
 
 pub struct DispatchRunner<T: 'static> {
-    wrapper: Wrapper<true, T, Sender<Closure<T>>, Closure<T>>,
+    wrapper: Wrapper<T, Sender<Closure<T>>, Closure<T>>,
     receiver: Receiver<Closure<T>>,
 }
 

src/platform_impl/web/async/waker.rs

@@ -6,9 +6,9 @@ use std::task::Poll;
 use super::super::main_thread::MainThreadMarker;
 use super::{AtomicWaker, Wrapper};
 
-pub struct WakerSpawner<T: 'static>(Wrapper<false, Handler<T>, Sender, usize>);
+pub struct WakerSpawner<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
 
-pub struct Waker<T: 'static>(Wrapper<false, Handler<T>, Sender, usize>);
+pub struct Waker<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
 
 struct Handler<T> {
     value: T,

src/platform_impl/web/async/wrapper.rs

@@ -6,14 +6,14 @@ use std::sync::Arc;
 
 // Unsafe wrapper type that allows us to use `T` when it's not `Send` from other threads.
 // `value` **must** only be accessed on the main thread.
-pub struct Wrapper<const SYNC: bool, V: 'static, S: Clone + Send, E> {
-    value: Value<SYNC, V>,
+pub struct Wrapper<V: 'static, S: Clone + Send, E> {
+    value: Value<V>,
     handler: fn(&RefCell<Option<V>>, E),
     sender_data: S,
     sender_handler: fn(&S, E),
 }
 
-struct Value<const SYNC: bool, V> {
+struct Value<V> {
     // SAFETY:
     // This value must not be accessed if not on the main thread.
     //
@@ -28,11 +28,11 @@ struct Value<const SYNC: bool, V> {
 }
 
 // SAFETY: See `Self::value`.
-unsafe impl<const SYNC: bool, V> Send for Value<SYNC, V> {}
+unsafe impl<V> Send for Value<V> {}
 // SAFETY: See `Self::value`.
-unsafe impl<V> Sync for Value<true, V> {}
+unsafe impl<V> Sync for Value<V> {}
 
-impl<const SYNC: bool, V, S: Clone + Send, E> Wrapper<SYNC, V, S, E> {
+impl<V, S: Clone + Send, E> Wrapper<V, S, E> {
     #[track_caller]
     pub fn new<R: Future<Output = ()>>(
         _: MainThreadMarker,
@@ -81,7 +81,7 @@ impl<const SYNC: bool, V, S: Clone + Send, E> Wrapper<SYNC, V, S, E> {
     }
 }
 
-impl<const SYNC: bool, V, S: Clone + Send, E> Clone for Wrapper<SYNC, V, S, E> {
+impl<V, S: Clone + Send, E> Clone for Wrapper<V, S, E> {
     fn clone(&self) -> Self {
         Self {
             value: Value {

tests/send_objects.rs

@@ -5,7 +5,7 @@ fn needs_send<T: Send>() {}
 fn event_loop_proxy_send() {
     #[allow(dead_code)]
     fn is_send<T: 'static + Send>() {
-        // ensures that `winit::EventLoopProxy` implements `Send`
+        // ensures that `winit::EventLoopProxy<T: Send>` implements `Send`
         needs_send::<winit::event_loop::EventLoopProxy<T>>();
     }
 }

tests/sync_object.rs

@@ -1,6 +1,15 @@
 #[allow(dead_code)]
 fn needs_sync<T: Sync>() {}
 
+#[test]
+fn event_loop_proxy_send() {
+    #[allow(dead_code)]
+    fn is_send<T: 'static + Send>() {
+        // ensures that `winit::EventLoopProxy<T: Send>` implements `Sync`
+        needs_sync::<winit::event_loop::EventLoopProxy<T>>();
+    }
+}
+
 #[test]
 fn window_sync() {
     // ensures that `winit::Window` implements `Sync`