apple: Implement wake-ups using system mechanisms (#4146)

Do the wake-up inside the perform callback on `CFRunLoopSource`.

src/platform_impl/apple/appkit/app_state.rs

@@ -1,7 +1,6 @@
 use std::cell::{Cell, OnceCell, RefCell};
 use std::mem;
 use std::rc::{Rc, Weak};
-use std::sync::atomic::Ordering as AtomicOrdering;
 use std::sync::Arc;
 use std::time::Instant;
 
@@ -11,7 +10,8 @@ use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy, NSRunningAppli
 use objc2_foundation::NSNotification;
 
 use super::super::event_handler::EventHandler;
-use super::event_loop::{stop_app_immediately, ActiveEventLoop, EventLoopProxy, PanicInfo};
+use super::super::event_loop_proxy::EventLoopProxy;
+use super::event_loop::{stop_app_immediately, ActiveEventLoop, PanicInfo};
 use super::menu;
 use super::observer::{EventLoopWaker, RunLoop};
 use crate::application::ApplicationHandler;
@@ -59,13 +59,17 @@ impl AppState {
         default_menu: bool,
         activate_ignoring_other_apps: bool,
     ) -> Rc<Self> {
-        let this = Rc::new(AppState {
+        let event_loop_proxy = Arc::new(EventLoopProxy::new(mtm, move || {
+            Self::get(mtm).with_handler(|app, event_loop| app.proxy_wake_up(event_loop));
+        }));
+
+        let this = Rc::new(Self {
             mtm,
             activation_policy,
-            event_loop_proxy: Arc::new(EventLoopProxy::new()),
             default_menu,
             activate_ignoring_other_apps,
             run_loop: RunLoop::main(mtm),
+            event_loop_proxy,
             event_handler: EventHandler::new(),
             stop_on_launch: Cell::new(false),
             stop_before_wait: Cell::new(false),
@@ -351,10 +355,6 @@ impl AppState {
             return;
         }
 
-        if self.event_loop_proxy.wake_up.swap(false, AtomicOrdering::Relaxed) {
-            self.with_handler(|app, event_loop| app.proxy_wake_up(event_loop));
-        }
-
         let redraw = mem::take(&mut *self.pending_redraw.borrow_mut());
         for window_id in redraw {
             self.with_handler(|app, event_loop| {

src/platform_impl/apple/appkit/event_loop.rs

@@ -1,10 +1,7 @@
 use std::any::Any;
 use std::cell::Cell;
-use std::os::raw::c_void;
 use std::panic::{catch_unwind, resume_unwind, RefUnwindSafe, UnwindSafe};
-use std::ptr;
 use std::rc::{Rc, Weak};
-use std::sync::atomic::{AtomicBool, Ordering as AtomicOrdering};
 use std::sync::Arc;
 use std::time::{Duration, Instant};
 
@@ -15,11 +12,6 @@ use objc2_app_kit::{
     NSApplication, NSApplicationActivationPolicy, NSApplicationDidFinishLaunchingNotification,
     NSApplicationWillTerminateNotification, NSWindow,
 };
-use objc2_core_foundation::{
-    kCFRunLoopCommonModes, CFIndex, CFRetained, CFRunLoopAddSource, CFRunLoopGetMain,
-    CFRunLoopSource, CFRunLoopSourceContext, CFRunLoopSourceCreate, CFRunLoopSourceSignal,
-    CFRunLoopWakeUp,
-};
 use objc2_foundation::{NSNotificationCenter, NSObjectProtocol};
 use rwh_06::HasDisplayHandle;
 
@@ -34,8 +26,7 @@ use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, RequestError};
 use crate::event_loop::{
     ActiveEventLoop as RootActiveEventLoop, ControlFlow, DeviceEvents,
-    EventLoopProxy as CoreEventLoopProxy, EventLoopProxyProvider,
-    OwnedDisplayHandle as CoreOwnedDisplayHandle,
+    EventLoopProxy as CoreEventLoopProxy, OwnedDisplayHandle as CoreOwnedDisplayHandle,
 };
 use crate::monitor::MonitorHandle as RootMonitorHandle;
 use crate::platform::macos::ActivationPolicy;
@@ -429,54 +420,3 @@ pub fn stop_app_on_panic<F: FnOnce() -> R + UnwindSafe, R>(
         },
     }
 }
-
-#[derive(Debug)]
-pub struct EventLoopProxy {
-    pub(crate) wake_up: AtomicBool,
-    source: CFRetained<CFRunLoopSource>,
-}
-
-unsafe impl Send for EventLoopProxy {}
-unsafe impl Sync for EventLoopProxy {}
-
-impl EventLoopProxy {
-    pub(crate) fn new() -> Self {
-        unsafe {
-            // just wake up the eventloop
-            extern "C-unwind" fn event_loop_proxy_handler(_context: *mut c_void) {}
-
-            // adding a Source to the main CFRunLoop lets us wake it up and
-            // process user events through the normal OS EventLoop mechanisms.
-            let rl = CFRunLoopGetMain().unwrap();
-            let mut context = CFRunLoopSourceContext {
-                version: 0,
-                info: ptr::null_mut(),
-                retain: None,
-                release: None,
-                copyDescription: None,
-                equal: None,
-                hash: None,
-                schedule: None,
-                cancel: None,
-                perform: Some(event_loop_proxy_handler),
-            };
-            let source = CFRunLoopSourceCreate(None, CFIndex::MAX - 1, &mut context).unwrap();
-            CFRunLoopAddSource(&rl, Some(&source), kCFRunLoopCommonModes);
-            CFRunLoopWakeUp(&rl);
-
-            EventLoopProxy { wake_up: AtomicBool::new(false), source }
-        }
-    }
-}
-
-impl EventLoopProxyProvider for EventLoopProxy {
-    fn wake_up(&self) {
-        self.wake_up.store(true, AtomicOrdering::Relaxed);
-        unsafe {
-            // Let the main thread know there's a new event.
-            CFRunLoopSourceSignal(&self.source);
-            let rl = CFRunLoopGetMain().unwrap();
-            CFRunLoopWakeUp(&rl);
-        }
-    }
-}

src/platform_impl/apple/event_loop_proxy.rs

@@ -0,0 +1,126 @@
+use std::os::raw::c_void;
+use std::sync::Arc;
+
+use objc2::MainThreadMarker;
+use objc2_core_foundation::{
+    kCFRunLoopCommonModes, CFIndex, CFRetained, CFRunLoop, CFRunLoopAddSource, CFRunLoopGetMain,
+    CFRunLoopSource, CFRunLoopSourceContext, CFRunLoopSourceCreate, CFRunLoopSourceInvalidate,
+    CFRunLoopSourceSignal, CFRunLoopWakeUp,
+};
+
+use crate::event_loop::EventLoopProxyProvider;
+
+/// A waker that signals a `CFRunLoopSource` on the main thread.
+///
+/// We use this to integrate with the system as cleanly as possible (instead of e.g. keeping an
+/// atomic around that we check on each iteration of the event loop).
+///
+/// See <https://developer.apple.com/documentation/corefoundation/cfrunloopsource?language=objc>.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub(crate) struct EventLoopProxy {
+    source: CFRetained<CFRunLoopSource>,
+    /// Cached value of `CFRunLoopGetMain`.
+    main_loop: CFRetained<CFRunLoop>,
+}
+
+// FIXME(madsmtm): Mark `CFRunLoopSource` + `CFRunLoop` as `Send` + `Sync`.
+unsafe impl Send for EventLoopProxy {}
+unsafe impl Sync for EventLoopProxy {}
+
+impl EventLoopProxy {
+    /// Create a new proxy, registering it to be performed on the main thread.
+    ///
+    /// The provided closure should call `proxy_wake_up` on the application.
+    pub(crate) fn new<F: Fn() + 'static>(mtm: MainThreadMarker, signaller: F) -> Self {
+        // We use an `Arc` here to make sure that the reference-counting of the signal container is
+        // atomic (`Retained`/`CFRetained` would be valid alternatives too).
+        let signaller = Arc::new(signaller);
+
+        unsafe extern "C-unwind" fn retain<F>(info: *const c_void) -> *const c_void {
+            // SAFETY: The pointer was passed to `CFRunLoopSourceContext.info` below.
+            unsafe { Arc::increment_strong_count(info.cast::<F>()) };
+            info
+        }
+        unsafe extern "C-unwind" fn release<F>(info: *const c_void) {
+            // SAFETY: The pointer was passed to `CFRunLoopSourceContext.info` below.
+            unsafe { Arc::decrement_strong_count(info.cast::<F>()) };
+        }
+
+        // Pointer equality / hashing.
+        extern "C-unwind" fn equal(info1: *const c_void, info2: *const c_void) -> u8 {
+            (info1 == info2) as u8
+        }
+        extern "C-unwind" fn hash(info: *const c_void) -> usize {
+            info as usize
+        }
+
+        // Call the provided closure.
+        unsafe extern "C-unwind" fn perform<F: Fn()>(info: *mut c_void) {
+            // SAFETY: The pointer was passed to `CFRunLoopSourceContext.info` below.
+            let signaller = unsafe { &*info.cast::<F>() };
+            (signaller)();
+        }
+
+        // Fire last.
+        let order = CFIndex::MAX - 1;
+
+        // This is marked `mut` to match the signature of `CFRunLoopSourceCreate`, but the
+        // information is copied, and not actually mutated.
+        let mut context = CFRunLoopSourceContext {
+            version: 0,
+            // This is retained on creation.
+            info: Arc::as_ptr(&signaller) as *mut c_void,
+            retain: Some(retain::<F>),
+            release: Some(release::<F>),
+            copyDescription: None,
+            equal: Some(equal),
+            hash: Some(hash),
+            schedule: None,
+            cancel: None,
+            perform: Some(perform::<F>),
+        };
+
+        // SAFETY: The normal callbacks are thread-safe (`retain`/`release` use atomics, and
+        // `equal`/`hash` only access a pointer).
+        //
+        // Note that the `perform` callback isn't thread-safe (we don't have `F: Send + Sync`), but
+        // that's okay, since we are on the main thread, and the source is only added to the main
+        // run loop (below), and hence only performed there.
+        //
+        // Keeping the closure alive beyond this scope is fine, because `F: 'static`.
+        let source = unsafe {
+            let _ = mtm;
+            CFRunLoopSourceCreate(None, order, &mut context).unwrap()
+        };
+
+        // Register the source to be performed on the main thread.
+        let main_loop = unsafe { CFRunLoopGetMain() }.unwrap();
+        unsafe { CFRunLoopAddSource(&main_loop, Some(&source), kCFRunLoopCommonModes) };
+
+        Self { source, main_loop }
+    }
+
+    // FIXME(madsmtm): Use this on macOS too.
+    // More difficult there, since the user can re-start the event loop.
+    #[cfg_attr(target_os = "macos", allow(dead_code))]
+    pub(crate) fn invalidate(&self) {
+        // NOTE: We do NOT fire this on `Drop`, since we want the proxy to be cloneable, such that
+        // we only need to register a single source even if there's multiple proxies in use.
+        unsafe { CFRunLoopSourceInvalidate(&self.source) };
+    }
+}
+
+impl EventLoopProxyProvider for EventLoopProxy {
+    fn wake_up(&self) {
+        // Signal the source, which ends up later invoking `perform` on the main thread.
+        //
+        // Multiple signals in quick succession are automatically coalesced into a single signal.
+        unsafe { CFRunLoopSourceSignal(&self.source) };
+
+        // Let the main thread know there's a new event.
+        //
+        // This is required since we may be (probably are) running on a different thread, and the
+        // main loop may be sleeping (and `CFRunLoopSourceSignal` won't wake it).
+        unsafe { CFRunLoopWakeUp(&self.main_loop) };
+    }
+}

src/platform_impl/apple/mod.rs

@@ -3,6 +3,7 @@
 #[cfg(target_os = "macos")]
 mod appkit;
 mod event_handler;
+mod event_loop_proxy;
 mod notification_center;
 #[cfg(not(target_os = "macos"))]
 mod uikit;

src/platform_impl/apple/uikit/app_state.rs

@@ -3,7 +3,6 @@
 use std::cell::{OnceCell, RefCell, RefMut};
 use std::collections::HashSet;
 use std::os::raw::c_void;
-use std::sync::atomic::Ordering;
 use std::sync::{Arc, Mutex};
 use std::time::Instant;
 use std::{mem, ptr};
@@ -19,8 +18,9 @@ use objc2_core_foundation::{
 use objc2_ui_kit::{UIApplication, UICoordinateSpace, UIView};
 
 use super::super::event_handler::EventHandler;
+use super::super::event_loop_proxy::EventLoopProxy;
 use super::window::WinitUIWindow;
-use super::{ActiveEventLoop, EventLoopProxy};
+use super::ActiveEventLoop;
 use crate::application::ApplicationHandler;
 use crate::dpi::PhysicalSize;
 use crate::event::{StartCause, SurfaceSizeWriter, WindowEvent};
@@ -102,7 +102,7 @@ pub(crate) struct AppState {
 }
 
 impl AppState {
-    pub(crate) fn get_mut(_mtm: MainThreadMarker) -> RefMut<'static, AppState> {
+    pub(crate) fn get_mut(mtm: MainThreadMarker) -> RefMut<'static, AppState> {
         // basically everything in UIKit requires the main thread, so it's pointless to use the
         // std::sync APIs.
         // must be mut because plain `static` requires `Sync`
@@ -114,17 +114,21 @@ impl AppState {
         if guard.is_none() {
             #[inline(never)]
             #[cold]
-            fn init_guard(guard: &mut RefMut<'static, Option<AppState>>) {
+            fn init_guard(guard: &mut RefMut<'static, Option<AppState>>, mtm: MainThreadMarker) {
                 let waker = EventLoopWaker::new(unsafe { CFRunLoopGetMain().unwrap() });
+                let event_loop_proxy = Arc::new(EventLoopProxy::new(mtm, move || {
+                    get_handler(mtm).handle(|app| app.proxy_wake_up(&ActiveEventLoop { mtm }));
+                }));
+
                 **guard = Some(AppState {
                     app_state: Some(AppStateImpl::Initial { queued_gpu_redraws: HashSet::new() }),
                     control_flow: ControlFlow::default(),
                     waker,
-                    event_loop_proxy: Arc::new(EventLoopProxy::new()),
+                    event_loop_proxy,
                     queued_events: Vec::new(),
                 });
             }
-            init_guard(&mut guard);
+            init_guard(&mut guard, mtm);
         }
         RefMut::map(guard, |state| state.as_mut().unwrap())
     }
@@ -394,13 +398,8 @@ fn handle_user_events(mtm: MainThreadMarker) {
     if matches!(this.state(), AppStateImpl::ProcessingRedraws { .. }) {
         bug!("user events attempted to be sent out while `ProcessingRedraws`");
     }
-    let event_loop_proxy = this.event_loop_proxy().clone();
     drop(this);
 
-    if event_loop_proxy.wake_up.swap(false, Ordering::Relaxed) {
-        get_handler(mtm).handle(|app| app.proxy_wake_up(&ActiveEventLoop { mtm }));
-    }
-
     loop {
         let mut this = AppState::get_mut(mtm);
         let queued_events = mem::take(&mut this.queued_events);
@@ -412,10 +411,6 @@ fn handle_user_events(mtm: MainThreadMarker) {
         for event in queued_events {
             handle_wrapped_event(mtm, event);
         }
-
-        if event_loop_proxy.wake_up.swap(false, Ordering::Relaxed) {
-            get_handler(mtm).handle(|app| app.proxy_wake_up(&ActiveEventLoop { mtm }));
-        }
     }
 }
 
@@ -503,6 +498,10 @@ pub(crate) fn terminated(application: &UIApplication) {
     drop(this);
 
     get_handler(mtm).handle(|app| app.exiting(&ActiveEventLoop { mtm }));
+
+    let this = AppState::get_mut(mtm);
+    // Prevent EventLoopProxy from firing again.
+    this.event_loop_proxy.invalidate();
 }
 
 fn handle_wrapped_event(mtm: MainThreadMarker, event: EventWrapper) {

src/platform_impl/apple/uikit/event_loop.rs

@@ -1,16 +1,13 @@
 use std::ffi::{c_char, c_int, c_void};
 use std::ptr::{self, NonNull};
-use std::sync::atomic::{AtomicBool, Ordering as AtomicOrdering};
 use std::sync::Arc;
 
 use objc2::rc::Retained;
 use objc2::runtime::ProtocolObject;
 use objc2::{msg_send, ClassType, MainThreadMarker};
 use objc2_core_foundation::{
-    kCFRunLoopCommonModes, kCFRunLoopDefaultMode, CFIndex, CFRetained, CFRunLoopActivity,
-    CFRunLoopAddObserver, CFRunLoopAddSource, CFRunLoopGetMain, CFRunLoopObserver,
-    CFRunLoopObserverCreate, CFRunLoopSource, CFRunLoopSourceContext, CFRunLoopSourceCreate,
-    CFRunLoopSourceInvalidate, CFRunLoopSourceSignal, CFRunLoopWakeUp,
+    kCFRunLoopDefaultMode, CFIndex, CFRunLoopActivity, CFRunLoopAddObserver, CFRunLoopGetMain,
+    CFRunLoopObserver, CFRunLoopObserverCreate,
 };
 use objc2_foundation::{NSNotificationCenter, NSObjectProtocol};
 use objc2_ui_kit::{
@@ -29,8 +26,7 @@ use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, NotSupportedError, RequestError};
 use crate::event_loop::{
     ActiveEventLoop as RootActiveEventLoop, ControlFlow, DeviceEvents,
-    EventLoopProxy as CoreEventLoopProxy, EventLoopProxyProvider,
-    OwnedDisplayHandle as CoreOwnedDisplayHandle,
+    EventLoopProxy as CoreEventLoopProxy, OwnedDisplayHandle as CoreOwnedDisplayHandle,
 };
 use crate::monitor::MonitorHandle as RootMonitorHandle;
 use crate::platform_impl::Window;
@@ -277,62 +273,6 @@ impl EventLoop {
     }
 }
 
-pub struct EventLoopProxy {
-    pub(crate) wake_up: AtomicBool,
-    source: CFRetained<CFRunLoopSource>,
-}
-
-unsafe impl Send for EventLoopProxy {}
-unsafe impl Sync for EventLoopProxy {}
-
-impl Drop for EventLoopProxy {
-    fn drop(&mut self) {
-        unsafe { CFRunLoopSourceInvalidate(&self.source) };
-    }
-}
-
-impl EventLoopProxy {
-    pub(crate) fn new() -> EventLoopProxy {
-        unsafe {
-            // just wake up the eventloop
-            extern "C-unwind" fn event_loop_proxy_handler(_: *mut c_void) {}
-
-            // adding a Source to the main CFRunLoop lets us wake it up and
-            // process user events through the normal OS EventLoop mechanisms.
-            let rl = CFRunLoopGetMain().unwrap();
-            let mut context = CFRunLoopSourceContext {
-                version: 0,
-                info: ptr::null_mut(),
-                retain: None,
-                release: None,
-                copyDescription: None,
-                equal: None,
-                hash: None,
-                schedule: None,
-                cancel: None,
-                perform: Some(event_loop_proxy_handler),
-            };
-            let source = CFRunLoopSourceCreate(None, CFIndex::MAX - 1, &mut context).unwrap();
-            CFRunLoopAddSource(&rl, Some(&source), kCFRunLoopCommonModes);
-            CFRunLoopWakeUp(&rl);
-
-            EventLoopProxy { wake_up: AtomicBool::new(false), source }
-        }
-    }
-}
-
-impl EventLoopProxyProvider for EventLoopProxy {
-    fn wake_up(&self) {
-        self.wake_up.store(true, AtomicOrdering::Relaxed);
-        unsafe {
-            // let the main thread know there's a new event
-            CFRunLoopSourceSignal(&self.source);
-            let rl = CFRunLoopGetMain().unwrap();
-            CFRunLoopWakeUp(&rl);
-        }
-    }
-}
-
 fn setup_control_flow_observers() {
     unsafe {
         // begin is queued with the highest priority to ensure it is processed before other

src/platform_impl/apple/uikit/mod.rs

@@ -10,7 +10,7 @@ mod window;
 use std::fmt;
 
 pub(crate) use self::event_loop::{
-    ActiveEventLoop, EventLoop, EventLoopProxy, PlatformSpecificEventLoopAttributes,
+    ActiveEventLoop, EventLoop, PlatformSpecificEventLoopAttributes,
 };
 pub(crate) use self::monitor::MonitorHandle;
 pub(crate) use self::window::{PlatformSpecificWindowAttributes, Window};