bevy/crates/bevy_app/src/schedule_runner.rs

use super::{App, AppBuilder, AppPlugin, GetEventReader};
use crate::{AppExit, Events};
use std::{thread, time::Duration};

#[derive(Copy, Clone, Debug)]
pub enum RunMode {
    Loop { wait: Option<Duration> },
    Once,
}

impl Default for RunMode {
    fn default() -> Self {
        RunMode::Loop { wait: None }
    }
}

#[derive(Default)]
pub struct ScheduleRunnerPlugin {
    pub run_mode: RunMode,
}

impl AppPlugin for ScheduleRunnerPlugin {
    fn build(&self, app: &mut AppBuilder) {
        let run_mode = self.run_mode;
        app.set_runner(move |mut app: App| {
            let mut app_exit_event_reader = app.resources.get_event_reader::<AppExit>();
            match run_mode {
                RunMode::Once => {
                    if let Some(ref mut schedule) = app.schedule {
                        schedule.execute(&mut app.world, &mut app.resources);
                    }
                }
                RunMode::Loop { wait } => loop {
                    if let Some(app_exit_events) = app.resources.get_mut::<Events<AppExit>>() {
                        if app_exit_events.latest(&mut app_exit_event_reader).is_some() {
                            break;
                        }
                    }

                    if let Some(ref mut schedule) = app.schedule {
                        schedule.execute(&mut app.world, &mut app.resources);
                    }
                    if let Some(wait) = wait {
                        thread::sleep(wait);
                    }
                },
            }
        });
    }
}