Can't create event loop ondemand #2431
Description
I want to be able to open a window, use event_loop.run_return to process some events on it, then close it, and then later open another window. When I try this on my Mac, I find that the second time I run run_return I get Event::LoopDestroyed almost immediately, and the new window is destroyed. This is the code I'm running:
fn main() {
use winit::{
event::{Event, WindowEvent},
event_loop::EventLoop,
platform::run_return::EventLoopExtRunReturn,
window::WindowBuilder,
};
fn show_window(event_loop: &mut EventLoop<()>, window_name: &str) {
eprintln!("Creating window {:?}", window_name);
let window = WindowBuilder::new()
.with_title(window_name)
.build(event_loop)
.unwrap();
event_loop.run_return(|event, _, control_flow| {
control_flow.set_wait();
match event {
Event::LoopDestroyed => {
eprintln!("Event::LoopDestroyed.");
}
// Platform-dependent event handlers to workaround a winit bug
// See: https://github.com/rust-windowing/winit/issues/987
// See: https://github.com/rust-windowing/winit/issues/1619
Event::RedrawEventsCleared if cfg!(windows) => {
println!("rendering");
}
Event::RedrawRequested(_) if !cfg!(windows) => {
println!("rendering");
}
Event::WindowEvent { window_id, .. } if window_id != window.id() => {
// This can happen if we close a window, and then reopen a new one,
// or if we have multiple windows open.
eprintln!("Ignoring event to old window");
}
Event::WindowEvent {
event: WindowEvent::CloseRequested,
..
} => {
eprintln!("WindowEvent::CloseRequested");
control_flow.set_exit();
}
Event::WindowEvent {
event: WindowEvent::Destroyed,
..
} => {
eprintln!("WindowEvent::Destroyed");
control_flow.set_exit();
}
_ => (),
}
});
eprintln!("-----------------");
}
let mut event_loop = EventLoop::new();
show_window(&mut event_loop, "First Window");
show_window(&mut event_loop, "Second Window");
}And this is the output:
Creating window "First Window"
rendering
rendering
WindowEvent::CloseRequested
Event::LoopDestroyed.
-----------------
Creating window "Second Window"
rendering
rendering
Event::LoopDestroyed.
-----------------
The WindowEvent::CloseRequested is me closing the window, but the second window also closes without any reason.
According to @zu1k, this is also a problem on Windows, but there it can be fixed by adding the following code after the first run_return:
event_loop.run_return(|_, _, control_flow| {
control_flow.set_exit();
});Related issue: emilk/egui#1919
One very bad work-around is to calli run_return multiple times, like so:
let mut quit = false;
while !quit {
event_loop.run_return(|event, _, control_flow| {
// Only set `quit = true;` when we really want to close the window.
});
}This still spams Event::LoopDestroyed over and over again, but the window stays up. However, it uses up ALL the CPU of one core, so this is NOT a viable solution.