use std::{hint::black_box, time::Instant};
fn measure(mut f: impl FnMut(), iters: usize) -> (f64, f64, f64) {
    for _ in 0..1000 { f(); }
    let mut samples = Vec::new();
    for _ in 0..15 {
        let start = Instant::now();
        for _ in 0..iters { f(); }
        samples.push(start.elapsed().as_secs_f64() * 1e6 / iters as f64);
    }
    samples.sort_by(f64::total_cmp);
    (samples[7], samples[0], samples[14])
}
#[inline(never)]
fn install_empty(pool: &rayon::ThreadPool) -> usize {
    pool.install(|| black_box(7usize))
}
fn main() {
    let available = std::thread::available_parallelism().unwrap().get();
    println!("available_parallelism={available}; 15 batches x 10000 calls; us/call median [min,max]");
    println!("direct {:?}", measure(|| { black_box(black_box(7usize)); }, 10000));
    let mut counts = vec![1, 2, 8, available]; counts.sort(); counts.dedup();
    for n in counts {
        let pool = rayon::ThreadPoolBuilder::new().num_threads(n).build().unwrap();
        pool.broadcast(|_| { black_box(7usize); });
        let outside = measure(|| { black_box(install_empty(black_box(&pool))); }, 10000);
        let inside = pool.install(|| measure(|| { black_box(install_empty(black_box(&pool))); }, 10000));
        println!("threads={n} outside={outside:?} inside={inside:?}");
    }
}