Make WindowBuilder Send + Sync

Window builder is always accessed by winit on the thread event loop
is on, thus it's safe to mark the data it gets as `Send + Sync`.
Each unsafe object is marked individually as `Send + Sync` instead
of just implementing `Send` and `Sync` for the whole builder.

CHANGELOG.md

@@ -37,6 +37,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - On Wayland, support `Occluded` event with xdg-shell v6
 - Implement `AsFd`/`AsRawFd` for `EventLoop<T>` on X11 and Wayland.
 - **Breaking:** Bump `ndk` version to `0.8.0`, ndk-sys to `0.5.0`, `android-activity` to `0.5.0`.
+- Make `WindowBuilder` `Send + Sync`.
 
 # 0.29.1-beta
 

src/lib.rs

@@ -163,3 +163,18 @@ mod platform_impl;
 pub mod window;
 
 pub mod platform;
+
+/// Wrapper for objects which winit will access on the main thread so they are effectively `Send`
+/// and `Sync`, since they always excute on a single thread.
+///
+/// # Safety
+///
+/// Winit can run only one event loop at the time and the event loop itself is tied to some thread.
+/// The objects could be send across the threads, but once passed to winit, they execute on the
+/// mean thread if the platform demands it. Thus marking such objects as `Send + Sync` is safe.
+#[doc(hidden)]
+#[derive(Clone, Debug)]
+pub(crate) struct SendSyncWrapper<T>(pub(crate) T);
+
+unsafe impl<T> Send for SendSyncWrapper<T> {}
+unsafe impl<T> Sync for SendSyncWrapper<T> {}

src/platform/web.rs

@@ -31,6 +31,7 @@ use crate::event::Event;
 use crate::event_loop::EventLoop;
 use crate::event_loop::EventLoopWindowTarget;
 use crate::window::{Window, WindowBuilder};
+use crate::SendSyncWrapper;
 
 use web_sys::HtmlCanvasElement;
 
@@ -81,26 +82,22 @@ pub trait WindowBuilderExtWebSys {
 
 impl WindowBuilderExtWebSys for WindowBuilder {
     fn with_canvas(mut self, canvas: Option<HtmlCanvasElement>) -> Self {
-        self.platform_specific.canvas = canvas;
-
+        self.platform_specific.canvas = SendSyncWrapper(canvas);
         self
     }
 
     fn with_prevent_default(mut self, prevent_default: bool) -> Self {
         self.platform_specific.prevent_default = prevent_default;
-
         self
     }
 
     fn with_focusable(mut self, focusable: bool) -> Self {
         self.platform_specific.focusable = focusable;
-
         self
     }
 
     fn with_append(mut self, append: bool) -> Self {
         self.platform_specific.append = append;
-
         self
     }
 }

src/platform_impl/ios/view.rs

@@ -473,7 +473,7 @@ impl WinitUIWindow {
 
         this.setRootViewController(Some(view_controller));
 
-        match window_attributes.fullscreen.clone().map(Into::into) {
+        match window_attributes.fullscreen.0.clone().map(Into::into) {
             Some(Fullscreen::Exclusive(ref video_mode)) => {
                 let monitor = video_mode.monitor();
                 let screen = monitor.ui_screen(mtm);

src/platform_impl/ios/window.rs

@@ -422,7 +422,7 @@ impl Window {
         // TODO: transparency, visible
 
         let main_screen = UIScreen::main(mtm);
-        let fullscreen = window_attributes.fullscreen.clone().map(Into::into);
+        let fullscreen = window_attributes.fullscreen.0.clone().map(Into::into);
         let screen = match fullscreen {
             Some(Fullscreen::Exclusive(ref video_mode)) => video_mode.monitor.ui_screen(mtm),
             Some(Fullscreen::Borderless(Some(ref monitor))) => monitor.ui_screen(mtm),

src/platform_impl/linux/wayland/window/mod.rs

@@ -151,7 +151,7 @@ impl Window {
         window_state.set_resizable(attributes.resizable);
 
         // Set startup mode.
-        match attributes.fullscreen.map(Into::into) {
+        match attributes.fullscreen.0.map(Into::into) {
             Some(Fullscreen::Exclusive(_)) => {
                 warn!("`Fullscreen::Exclusive` is ignored on Wayland");
             }

src/platform_impl/linux/x11/window.rs

@@ -150,7 +150,7 @@ impl UnownedWindow {
         let xconn = &event_loop.xconn;
         let atoms = xconn.atoms();
         #[cfg(feature = "rwh_06")]
-        let root = match window_attrs.parent_window {
+        let root = match window_attrs.parent_window.0 {
             Some(rwh_06::RawWindowHandle::Xlib(handle)) => handle.window as xproto::Window,
             Some(rwh_06::RawWindowHandle::Xcb(handle)) => handle.window.get(),
             Some(raw) => unreachable!("Invalid raw window handle {raw:?} on X11"),
@@ -547,10 +547,10 @@ impl UnownedWindow {
             if window_attrs.maximized {
                 leap!(window.set_maximized_inner(window_attrs.maximized)).ignore_error();
             }
-            if window_attrs.fullscreen.is_some() {
+            if window_attrs.fullscreen.0.is_some() {
                 if let Some(flusher) =
                     leap!(window
-                        .set_fullscreen_inner(window_attrs.fullscreen.clone().map(Into::into)))
+                        .set_fullscreen_inner(window_attrs.fullscreen.0.clone().map(Into::into)))
                 {
                     flusher.ignore_error()
                 }

src/platform_impl/macos/window.rs

@@ -295,7 +295,7 @@ impl WinitWindow {
         trace_scope!("WinitWindow::new");
 
         let this = autoreleasepool(|_| {
-            let screen = match attrs.fullscreen.clone().map(Into::into) {
+            let screen = match attrs.fullscreen.0.clone().map(Into::into) {
                 Some(Fullscreen::Borderless(Some(monitor)))
                 | Some(Fullscreen::Exclusive(VideoMode { monitor, .. })) => {
                     monitor.ns_screen().or_else(NSScreen::main)
@@ -449,7 +449,7 @@ impl WinitWindow {
         .ok_or_else(|| os_error!(OsError::CreationError("Couldn't create `NSWindow`")))?;
 
         #[cfg(feature = "rwh_06")]
-        match attrs.parent_window {
+        match attrs.parent_window.0 {
             Some(rwh_06::RawWindowHandle::AppKit(handle)) => {
                 // SAFETY: Caller ensures the pointer is valid or NULL
                 // Unwrap is fine, since the pointer comes from `NonNull`.
@@ -520,14 +520,14 @@ impl WinitWindow {
             }
         }
 
-        let delegate = WinitWindowDelegate::new(&this, attrs.fullscreen.is_some());
+        let delegate = WinitWindowDelegate::new(&this, attrs.fullscreen.0.is_some());
 
         // XXX Send `Focused(false)` right after creating the window delegate, so we won't
         // obscure the real focused events on the startup.
         delegate.queue_event(WindowEvent::Focused(false));
 
         // Set fullscreen mode after we setup everything
-        this.set_fullscreen(attrs.fullscreen.map(Into::into));
+        this.set_fullscreen(attrs.fullscreen.0.map(Into::into));
 
         // Setting the window as key has to happen *after* we set the fullscreen
         // state, since otherwise we'll briefly see the window at normal size

src/platform_impl/web/web_sys/canvas.rs

@@ -63,7 +63,7 @@ impl Canvas {
         attr: &WindowAttributes,
         platform_attr: PlatformSpecificWindowBuilderAttributes,
     ) -> Result<Self, RootOE> {
-        let canvas = match platform_attr.canvas {
+        let canvas = match platform_attr.canvas.0 {
             Some(canvas) => canvas,
             None => document
                 .create_element("canvas")
@@ -127,7 +127,7 @@ impl Canvas {
             super::set_canvas_position(&common.document, &common.raw, &common.style, position);
         }
 
-        if attr.fullscreen.is_some() {
+        if attr.fullscreen.0.is_some() {
             common.fullscreen_handler.request_fullscreen();
         }
 

src/platform_impl/web/window.rs

@@ -5,6 +5,7 @@ use crate::window::{
     CursorGrabMode, CursorIcon, ImePurpose, ResizeDirection, Theme, UserAttentionType,
     WindowAttributes, WindowButtons, WindowId as RootWI, WindowLevel,
 };
+use crate::SendSyncWrapper;
 
 use web_sys::HtmlCanvasElement;
 
@@ -455,7 +456,7 @@ impl From<u64> for WindowId {
 
 #[derive(Clone)]
 pub struct PlatformSpecificWindowBuilderAttributes {
-    pub(crate) canvas: Option<backend::RawCanvasType>,
+    pub(crate) canvas: SendSyncWrapper<Option<backend::RawCanvasType>>,
     pub(crate) prevent_default: bool,
     pub(crate) focusable: bool,
     pub(crate) append: bool,
@@ -464,7 +465,7 @@ pub struct PlatformSpecificWindowBuilderAttributes {
 impl Default for PlatformSpecificWindowBuilderAttributes {
     fn default() -> Self {
         Self {
-            canvas: None,
+            canvas: SendSyncWrapper(None),
             prevent_default: true,
             focusable: true,
             append: false,

src/platform_impl/windows/window.rs

@@ -1185,8 +1185,8 @@ impl<'a, T: 'static> InitData<'a, T> {
 
         win.set_enabled_buttons(attributes.enabled_buttons);
 
-        if attributes.fullscreen.is_some() {
-            win.set_fullscreen(attributes.fullscreen.map(Into::into));
+        if attributes.fullscreen.0.is_some() {
+            win.set_fullscreen(attributes.fullscreen.0.map(Into::into));
             unsafe { force_window_active(win.window.0) };
         } else {
             let size = attributes
@@ -1272,7 +1272,7 @@ where
     };
 
     #[cfg(feature = "rwh_06")]
-    let parent = match attributes.parent_window {
+    let parent = match attributes.parent_window.0 {
         Some(rwh_06::RawWindowHandle::Win32(handle)) => {
             window_flags.set(WindowFlags::CHILD, true);
             if pl_attribs.menu.is_some() {

src/window.rs

@@ -6,7 +6,7 @@ use crate::{
     error::{ExternalError, NotSupportedError, OsError},
     event_loop::EventLoopWindowTarget,
     monitor::{MonitorHandle, VideoMode},
-    platform_impl,
+    platform_impl, SendSyncWrapper,
 };
 
 pub use crate::icon::{BadIcon, Icon};
@@ -141,7 +141,6 @@ pub struct WindowAttributes {
     pub resizable: bool,
     pub enabled_buttons: WindowButtons,
     pub title: String,
-    pub fullscreen: Option<Fullscreen>,
     pub maximized: bool,
     pub visible: bool,
     pub transparent: bool,
@@ -152,9 +151,10 @@ pub struct WindowAttributes {
     pub resize_increments: Option<Size>,
     pub content_protected: bool,
     pub window_level: WindowLevel,
-    #[cfg(feature = "rwh_06")]
-    pub parent_window: Option<rwh_06::RawWindowHandle>,
     pub active: bool,
+    #[cfg(feature = "rwh_06")]
+    pub(crate) parent_window: SendSyncWrapper<Option<rwh_06::RawWindowHandle>>,
+    pub(crate) fullscreen: SendSyncWrapper<Option<Fullscreen>>,
 }
 
 impl Default for WindowAttributes {
@@ -169,7 +169,7 @@ impl Default for WindowAttributes {
             enabled_buttons: WindowButtons::all(),
             title: "winit window".to_owned(),
             maximized: false,
-            fullscreen: None,
+            fullscreen: SendSyncWrapper(None),
             visible: true,
             transparent: false,
             blur: false,
@@ -180,12 +180,25 @@ impl Default for WindowAttributes {
             resize_increments: None,
             content_protected: false,
             #[cfg(feature = "rwh_06")]
-            parent_window: None,
+            parent_window: SendSyncWrapper(None),
             active: true,
         }
     }
 }
 
+impl WindowAttributes {
+    /// Get the parent window stored on the attributes.
+    #[cfg(feature = "rwh_06")]
+    pub fn parent_window(&self) -> Option<&rwh_06::RawWindowHandle> {
+        self.parent_window.0.as_ref()
+    }
+
+    /// Get `Fullscreen` option stored on the attributes.
+    pub fn fullscreen(&self) -> Option<&Fullscreen> {
+        self.fullscreen.0.as_ref()
+    }
+}
+
 impl WindowBuilder {
     /// Initializes a new builder with default values.
     #[inline]
@@ -303,7 +316,7 @@ impl WindowBuilder {
     /// See [`Window::set_fullscreen`] for details.
     #[inline]
     pub fn with_fullscreen(mut self, fullscreen: Option<Fullscreen>) -> Self {
-        self.window.fullscreen = fullscreen;
+        self.window.fullscreen = SendSyncWrapper(fullscreen);
         self
     }
 
@@ -479,7 +492,7 @@ impl WindowBuilder {
         mut self,
         parent_window: Option<rwh_06::RawWindowHandle>,
     ) -> Self {
-        self.window.parent_window = parent_window;
+        self.window.parent_window = SendSyncWrapper(parent_window);
         self
     }
 
@@ -1510,12 +1523,9 @@ impl Window {
 #[cfg(feature = "rwh_06")]
 impl rwh_06::HasWindowHandle for Window {
     fn window_handle(&self) -> Result<rwh_06::WindowHandle<'_>, rwh_06::HandleError> {
-        struct Wrapper(rwh_06::RawWindowHandle);
-        unsafe impl Send for Wrapper {}
-
         let raw = self
             .window
-            .maybe_wait_on_main(|w| w.raw_window_handle_rwh_06().map(Wrapper))?
+            .maybe_wait_on_main(|w| w.raw_window_handle_rwh_06().map(SendSyncWrapper))?
             .0;
 
         // SAFETY: The window handle will never be deallocated while the window is alive.
@@ -1526,12 +1536,9 @@ impl rwh_06::HasWindowHandle for Window {
 #[cfg(feature = "rwh_06")]
 impl rwh_06::HasDisplayHandle for Window {
     fn display_handle(&self) -> Result<rwh_06::DisplayHandle<'_>, rwh_06::HandleError> {
-        struct Wrapper(rwh_06::RawDisplayHandle);
-        unsafe impl Send for Wrapper {}
-
         let raw = self
             .window
-            .maybe_wait_on_main(|w| w.raw_display_handle_rwh_06().map(Wrapper))?
+            .maybe_wait_on_main(|w| w.raw_display_handle_rwh_06().map(SendSyncWrapper))?
             .0;
 
         // SAFETY: The window handle will never be deallocated while the window is alive.
@@ -1542,10 +1549,8 @@ impl rwh_06::HasDisplayHandle for Window {
 #[cfg(feature = "rwh_05")]
 unsafe impl rwh_05::HasRawWindowHandle for Window {
     fn raw_window_handle(&self) -> rwh_05::RawWindowHandle {
-        struct Wrapper(rwh_05::RawWindowHandle);
-        unsafe impl Send for Wrapper {}
         self.window
-            .maybe_wait_on_main(|w| Wrapper(w.raw_window_handle_rwh_05()))
+            .maybe_wait_on_main(|w| SendSyncWrapper(w.raw_window_handle_rwh_05()))
             .0
     }
 }
@@ -1557,21 +1562,17 @@ unsafe impl rwh_05::HasRawDisplayHandle for Window {
     ///
     /// [`EventLoop`]: crate::event_loop::EventLoop
     fn raw_display_handle(&self) -> rwh_05::RawDisplayHandle {
-        struct Wrapper(rwh_05::RawDisplayHandle);
-        unsafe impl Send for Wrapper {}
         self.window
-            .maybe_wait_on_main(|w| Wrapper(w.raw_display_handle_rwh_05()))
+            .maybe_wait_on_main(|w| SendSyncWrapper(w.raw_display_handle_rwh_05()))
             .0
     }
 }
 
 #[cfg(feature = "rwh_04")]
 unsafe impl rwh_04::HasRawWindowHandle for Window {
     fn raw_window_handle(&self) -> rwh_04::RawWindowHandle {
-        struct Wrapper(rwh_04::RawWindowHandle);
-        unsafe impl Send for Wrapper {}
         self.window
-            .maybe_wait_on_main(|w| Wrapper(w.raw_window_handle_rwh_04()))
+            .maybe_wait_on_main(|w| SendSyncWrapper(w.raw_window_handle_rwh_04()))
             .0
     }
 }

tests/send_objects.rs

@@ -16,6 +16,11 @@ fn window_send() {
     needs_send::<winit::window::Window>();
 }
 
+#[test]
+fn window_builder_send() {
+    needs_send::<winit::window::WindowBuilder>();
+}
+
 #[test]
 fn ids_send() {
     // ensures that the various `..Id` types implement `Send`

tests/sync_object.rs

@@ -6,3 +6,8 @@ fn window_sync() {
     // ensures that `winit::Window` implements `Sync`
     needs_sync::<winit::window::Window>();
 }
+
+#[test]
+fn window_builder_sync() {
+    needs_sync::<winit::window::WindowBuilder>();
+}