eframe/native/
event_loop_context.rs

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1use std::cell::Cell;
2use winit::event_loop::ActiveEventLoop;
3
4thread_local! {
5    static CURRENT_EVENT_LOOP: Cell<Option<*const ActiveEventLoop>> = const { Cell::new(None) };
6}
7
8struct EventLoopGuard;
9
10impl EventLoopGuard {
11    fn new(event_loop: &ActiveEventLoop) -> Self {
12        CURRENT_EVENT_LOOP.with(|cell| {
13            assert!(
14                cell.get().is_none(),
15                "Attempted to set a new event loop while one is already set"
16            );
17            cell.set(Some(std::ptr::from_ref::<ActiveEventLoop>(event_loop)));
18        });
19        Self
20    }
21}
22
23impl Drop for EventLoopGuard {
24    fn drop(&mut self) {
25        CURRENT_EVENT_LOOP.with(|cell| cell.set(None));
26    }
27}
28
29// Helper function to safely use the current event loop
30#[allow(unsafe_code)]
31pub fn with_current_event_loop<F, R>(f: F) -> Option<R>
32where
33    F: FnOnce(&ActiveEventLoop) -> R,
34{
35    CURRENT_EVENT_LOOP.with(|cell| {
36        cell.get().map(|ptr| {
37            // SAFETY:
38            // 1. The pointer is guaranteed to be valid when it's Some, as the EventLoopGuard that created it
39            //    lives at least as long as the reference, and clears it when it's dropped. Only run_with_event_loop creates
40            //    a new EventLoopGuard, and does not leak it.
41            // 2. Since the pointer was created from a borrow which lives at least as long as this pointer there are
42            //    no mutable references to the ActiveEventLoop.
43            let event_loop = unsafe { &*ptr };
44            f(event_loop)
45        })
46    })
47}
48
49// The only public interface to use the event loop
50pub fn with_event_loop_context(event_loop: &ActiveEventLoop, f: impl FnOnce()) {
51    // NOTE: For safety, this guard must NOT be leaked.
52    let _guard = EventLoopGuard::new(event_loop);
53    f();
54}
eframe/native/event_loop_context.rs

eframe/native/
event_loop_context.rs
