Implement AsFd/AsRawFd for EventLoop<T>

This should help other crates to integrate winit's event loop into
their bigger event loop without adding an extra thread.

CHANGELOG.md

@@ -34,6 +34,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 - On iOS, send events `WindowEvent::Occluded(false)`, `WindowEvent::Occluded(true)` when application enters/leaves foreground.
 - **Breaking** add `Event::MemoryWarning`; implemented on iOS/Android.
 - On Wayland, support `Occluded` event with xdg-shell v6
+- Implement `AsFd`/`AsRawFd` for `EventLoop<T>` on X11 and Wayland.
 
 # 0.29.1-beta
 

src/event_loop.rs

@@ -9,6 +9,8 @@
 //! handle events.
 use std::marker::PhantomData;
 use std::ops::Deref;
+#[cfg(any(x11_platform, wayland_platform))]
+use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
 use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
 use std::{error, fmt};
 
@@ -262,6 +264,34 @@ unsafe impl<T> rwh_05::HasRawDisplayHandle for EventLoop<T> {
     }
 }
 
+#[cfg(any(x11_platform, wayland_platform))]
+impl<T> AsFd for EventLoop<T> {
+    /// Get the underlying [EventLoop]'s `fd` which you can register
+    /// into other event loop, like [`calloop`] or [`mio`]. When doing so, the
+    /// loop must be polled with the [`pump_events`] API.
+    ///
+    /// [`calloop`]: https://crates.io/crates/calloop
+    /// [`mio`]: https://crates.io/crates/mio
+    /// [`pump_events`]: crate::platform::pump_events::EventLoopExtPumpEvents::pump_events
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        self.event_loop.as_fd()
+    }
+}
+
+#[cfg(any(x11_platform, wayland_platform))]
+impl<T> AsRawFd for EventLoop<T> {
+    /// Get the underlying [EventLoop]'s raw `fd` which you can register
+    /// into other event loop, like [`calloop`] or [`mio`]. When doing so, the
+    /// loop must be polled with the [`pump_events`] API.
+    ///
+    /// [`calloop`]: https://crates.io/crates/calloop
+    /// [`mio`]: https://crates.io/crates/mio
+    /// [`pump_events`]: crate::platform::pump_events::EventLoopExtPumpEvents::pump_events
+    fn as_raw_fd(&self) -> RawFd {
+        self.event_loop.as_raw_fd()
+    }
+}
+
 impl<T> Deref for EventLoop<T> {
     type Target = EventLoopWindowTarget<T>;
     fn deref(&self) -> &EventLoopWindowTarget<T> {

src/platform_impl/linux/mod.rs

@@ -3,6 +3,7 @@
 #[cfg(all(not(x11_platform), not(wayland_platform)))]
 compile_error!("Please select a feature to build for unix: `x11`, `wayland`");
 
+use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
 use std::sync::Arc;
 use std::time::Duration;
 use std::{collections::VecDeque, env, fmt};
@@ -827,6 +828,18 @@ impl<T: 'static> EventLoop<T> {
     }
 }
 
+impl<T> AsFd for EventLoop<T> {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.as_fd())
+    }
+}
+
+impl<T> AsRawFd for EventLoop<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.as_raw_fd())
+    }
+}
+
 impl<T: 'static> EventLoopProxy<T> {
     pub fn send_event(&self, event: T) -> Result<(), EventLoopClosed<T>> {
         x11_or_wayland!(match self; EventLoopProxy(proxy) => proxy.send_event(event))

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

@@ -4,6 +4,7 @@ use std::cell::{Cell, RefCell};
 use std::io::Result as IOResult;
 use std::marker::PhantomData;
 use std::mem;
+use std::os::unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd};
 use std::rc::Rc;
 use std::sync::atomic::Ordering;
 use std::sync::{Arc, Mutex};
@@ -589,6 +590,18 @@ impl<T: 'static> EventLoop<T> {
     }
 }
 
+impl<T> AsFd for EventLoop<T> {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        self.event_loop.as_fd()
+    }
+}
+
+impl<T> AsRawFd for EventLoop<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.event_loop.as_raw_fd()
+    }
+}
+
 pub struct EventLoopWindowTarget<T> {
     /// The event loop wakeup source.
     pub event_loop_awakener: calloop::ping::Ping,

src/platform_impl/linux/x11/mod.rs

@@ -32,7 +32,7 @@ use std::{
     ops::Deref,
     os::{
         raw::*,
-        unix::io::{AsRawFd, BorrowedFd},
+        unix::io::{AsFd, AsRawFd, BorrowedFd, RawFd},
     },
     ptr,
     rc::Rc,
@@ -658,6 +658,18 @@ impl<T: 'static> EventLoop<T> {
     }
 }
 
+impl<T> AsFd for EventLoop<T> {
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        self.event_loop.as_fd()
+    }
+}
+
+impl<T> AsRawFd for EventLoop<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.event_loop.as_raw_fd()
+    }
+}
+
 pub(crate) fn get_xtarget<T>(target: &RootELW<T>) -> &EventLoopWindowTarget<T> {
     match target.p {
         super::EventLoopWindowTarget::X(ref target) => target,