Platform

Platform: Linux with X11. The same code works on Windows.

Issue

• Calling Window::request_redraw() at all while handling EventsCleared causes an event stalling issue where events are very delayed.
• Calling Window::request_redraw() while handling RedrawRequested freezes the program. Fixed by winit PR 1046
• Calling Window::request_redraw() causes a large delay in event processing.

Possible Cause

I'm unsure if the issues are related but I believe I found the cause to the second issue and I believe it to be a deadlock on a Mutex. The implementation of EventLoop's has a Mutex field called pending_redraws that is locked when dispatching RedrawRequested events. Because of this when I try and request a redraw after the frame is over during the RedrawRequested event handler, the Mutex is still locked and a deadlock occurs when trying to acquire it as Window::request_redraw tries to do so.

https://github.com/rust-windowing/winit/blob/master/src/platform_impl/linux/x11/mod.rs#L281
https://github.com/rust-windowing/winit/blob/master/src/platform_impl/linux/x11/window.rs#L1288