Reducing CPU usage for mostly idle non-game applications by parking the main thread

[evanrelf]

I'm toying with the idea of using Bevy for my terminal-based text editor. I noticed in my experiments that Bevy pegs at least one of my CPU cores (i.e. >100% utilization) even if there's no work to do. This happens even with App::new().add_plugins(MinimalPlugins).run().

Based on previous work on this text editor project, I know that the program is idle most of the time, and only does work in response to a limited number of external inputs that I know and control. So I thought... maybe this is crazy, but... what if I just park the main thread, stopping Bevy from spinning pointlessly, until I know I have work to do? If I receive inputs from the outside world on a separate thread, I can have it wait for stimulus, and then feed Bevy that input + unpark the main thread.

This is working really well for my extremely early experiments! Thought I would share in case someone else would benefit, or someone has feedback on how I could improve this / achieve this differently / think better of this 🙂

https://github.com/evanrelf/indigo/blob/d01c3cc12e099c942070eefac68dd6a032e8d4a2/crates/indigo-bevy/src/park.rs

Some other info:

• This brings CPU utilization when active below 30% on average, and down to 0% when idle.
• Unparking the main thread happens ~instantly; there's no perceptible input lag.
• I have most of Bevy's feature flags turned off, and I'm rendering to the terminal with the ratatui crate.
• I'm on macOS Sequoia 15.4.1

[mockersf]

This is something that Bevy supports if you're using winit by setting the WinitSettings resource

[evanrelf]

Nice. In my case, I don't have a GUI window because I'm rendering a TUI in the terminal with ratatui.