Use threadpool with messages

---

• threadpool
• Using channel messages to let the main thread know the processing is done.

examples/threads/use-threadpool-with-messages/src/main.rs

use std::sync::mpsc::channel;
use threadpool::ThreadPool;

fn main() {
    let numbers = (0..100).collect::<Vec<u32>>();
    //numbers.iter().map(|val| do_something(*val)).for_each(drop);

    let n_workers = 4;
    let pool = ThreadPool::new(n_workers);

    let (tx, rx) = channel();
    let count = numbers.len();
    for num in numbers {
        let tx = tx.clone();
        pool.execute(move || {
            do_something(num);
            tx.send(1)
                .expect("channel will be there waiting for the pool");
        });
    }

    #[allow(clippy::unnecessary_fold)]
    let result = rx.iter().take(count).fold(0, |a, b| a + b);

    assert_eq!(result, count);
}

fn do_something(num: u32) {
    println!("{} {:?}", num, std::thread::current().id());
}