x11: switch from wait_for_event() to directly using poll()

Cargo.toml

@@ -18,6 +18,7 @@ raw-window-handle = "0.3.3"
 xcb = { version = "0.9", features = ["thread", "xlib_xcb", "dri2"] }
 x11 = { version = "2.18", features = ["xlib"] }
 libc = "0.2"
+nix = "0.18"
 
 [target.'cfg(target_os="windows")'.dependencies]
 winapi = { version = "0.3.8", features = ["libloaderapi", "winuser", "windef", "minwindef", "guiddef", "combaseapi", "wingdi", "errhandlingapi"] }

src/x11/window.rs

@@ -1,9 +1,10 @@
 use std::os::raw::{c_ulong, c_void};
 
+use raw_window_handle::{unix::XlibHandle, HasRawWindowHandle, RawWindowHandle};
+
 use super::XcbConnection;
 use crate::{Event, MouseButtonID, MouseScroll, Parent, WindowHandler, WindowOpenOptions};
 
-use raw_window_handle::{unix::XlibHandle, HasRawWindowHandle, RawWindowHandle};
 
 pub struct Window {
     xcb_connection: XcbConnection,
@@ -101,14 +102,43 @@ impl Window {
         WindowHandle
     }
 
-    // Event loop
-    fn run_event_loop<H: WindowHandler>(&mut self, handler: &mut H) {
-        loop {
-            let ev = self.xcb_connection.conn.wait_for_event();
-            if let Some(event) = ev {
+    #[inline]
+    fn drain_xcb_events<H: WindowHandler>(&mut self, handler: &mut H) {
+        while let Some(event) = self.xcb_connection.conn.poll_for_event() {
             self.handle_xcb_event(handler, event);
         }
     }
+
+    // Event loop
+    // FIXME: poll() acts fine on linux, sometimes funky on *BSD. XCB upstream uses a define to
+    // switch between poll() and select() (the latter of which is fine on *BSD), and we should do
+    // the same.
+    fn run_event_loop<H: WindowHandler>(&mut self, handler: &mut H) {
+        use nix::poll::*;
+
+        let xcb_fd = unsafe {
+            let raw_conn = self.xcb_connection.conn.get_raw_conn();
+            xcb::ffi::xcb_get_file_descriptor(raw_conn)
+        };
+
+        loop {
+            let mut fds = [
+                PollFd::new(xcb_fd, PollFlags::POLLIN)
+            ];
+
+            // FIXME: handle errors
+            poll(&mut fds, -1).unwrap();
+
+            if let Some(revents) = fds[0].revents() {
+                if revents.contains(PollFlags::POLLERR) {
+                    panic!("xcb connection poll error");
+                }
+
+                if revents.contains(PollFlags::POLLIN) {
+                    self.drain_xcb_events(handler);
+                }
+            }
+        }
     }
 
     fn handle_xcb_event<H: WindowHandler>(&mut self, handler: &mut H, event: xcb::GenericEvent) {