You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: busy_behavior.rs
    path of file: ./repos/bevy/crates/bevy_tasks/examples
    
    the code of the file until where you have to start completion: //! 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 r
    
fn main() {
    let pool = TaskPoolBuilder::new()
        .thread_name("Busy Behavior ThreadPool".to_string())
        .num_threads(4)
        .build();

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

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

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