bevy/crates/bevy_tasks/examples/busy_behavior.rs

use bevy_tasks::TaskPoolBuilder;

// This sample demonstrates creating a thread pool with 4 tasks and spawning 40 tasks that spin
// for 100ms. It's expected to take about a second to run (assuming the machine has >= 4 logical
// cores)

fn main() {
    let pool = TaskPoolBuilder::new()
        .thread_name("Busy Behavior ThreadPool".to_string())
        .num_threads(4)
        .build();

    let t0 = instant::Instant::now();
    pool.scope(|s| {
        for i in 0..40 {
            s.spawn(async move {
                let now = instant::Instant::now();
                while instant::Instant::now() - now < instant::Duration::from_millis(100) {
                    // spin, simulating work being done
                }

                println!(
                    "Thread {:?} index {} finished",
                    std::thread::current().id(),
                    i
                );
            })
        }
    });

    let t1 = instant::Instant::now();
    println!("all tasks finished in {} secs", (t1 - t0).as_secs_f32());
}