quest – Rust: Channels

Systems Advanced

19 Channels

Instead of sharing memory, pass messages. An mpsc channel has many senders and one receiver. When every sender is dropped, iterating the receiver ends -- that is how the loop knows to stop.

Step 2 / 2

In fan_in, spawn workers threads where worker i sends i * 10. Collect everything received into a sorted vec.

Hints

Clone the sender for each worker: let tx = tx.clone();.
Drop the original tx before collecting, or the receiver waits forever for a sender that never sends.

19_channels.rs

use std::sync::mpsc;
use std::thread;

// worker i sends i*10; collect all results, sorted ascending
fn fan_in(workers: i32) -> Vec<i32> {
    todo!()
}

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Reveal solution

use std::sync::mpsc;
use std::thread;

fn fan_in(workers: i32) -> Vec<i32> {
    let (tx, rx) = mpsc::channel();
    for i in 0..workers {
        let tx = tx.clone();
        thread::spawn(move || {
            tx.send(i * 10).unwrap();
        });
    }
    drop(tx); // drop the last original sender so rx iteration ends
    let mut got: Vec<i32> = rx.iter().collect();
    got.sort();
    got
}