Beauty of Rust

channels.rs

use std::char;
use std::collections::HashMap;
use std::thread;
use std::sync::{Arc, Barrier};
use std::sync::mpsc::{channel, Sender};

const NTHREADS: u32 = 5;

fn slow(n: u32) -> char {
    thread::sleep_ms(n);
    let chr = char::from_u32(n % 26 + 65).unwrap();
    chr
}

fn main() {
    println!("[start]");

    // poor man's actor
    let (mem_tx, mem_rx) = channel::<(u32, Sender<char>)>();
    thread::spawn(move|| {
        let mut mem = HashMap::new();
        for (n, tx) in mem_rx.iter() {
            let chr = *mem.entry(n).or_insert_with(|| { slow(n) });
            tx.send(chr).unwrap();
        }
    });

    for pass in 0..3 {
        let barrier = Arc::new(Barrier::new((NTHREADS as usize) + 1));
        for i in 0..NTHREADS {
            let n = (i + 1) * 500;
            let bc = barrier.clone();
            let mem_txc = mem_tx.clone();
            thread::spawn(move|| {
                let (tx, rx) = channel::<char>();
                mem_txc.send((n, tx)).unwrap();
                let chr = rx.recv().unwrap();
                println!("pass {}: slow({}) = {}", pass, n, chr);
                bc.wait();
                println!("[thread {} about to die]", i);
            });
        }
        barrier.wait();
    }
    // join threads here
    println!("[end]");
}