スレッド間通信でchannelを使う(@Rust)

use std::thread;
use std::time::Duration;
use std::sync::mpsc;

fn main() {
    let (tx, rx) = mpsc::channel();
    let mut handles = Vec::new();
    for i in 0..3 {
        let thread_tx = tx.clone();
        let handle = thread::spawn(move || {
            for j in 1..10 {
                println!("hi number {} {} from the spawned thread!", i, j);
                thread::sleep(Duration::from_millis(1));
            }
            thread_tx.send(i).unwrap();
        });
        handles.push(handle);
    }

    for i in 1..5 {
        println!("hi number {} from the main thread!", i);
        thread::sleep(Duration::from_millis(1));
    }

    for handle in handles {
        handle.join().unwrap();
    }

    drop(tx);       // without drop(), this program doesn't terminate, wait for tx forever

    for received in rx {
        println!("Got from the threads : {}", received);
    }

}

~~~~~~
hi number 0 9 from the spawned thread!
hi number 2 9 from the spawned thread!
Got from the threads : 0
Got from the threads : 1
Got from the threads : 2