Rust Brain Teasers

Puzzle 19

Sleepless in Tokio

sleepless/Cargo.toml

[package]
name = "sleepless"
version = "0.1.0"
edition = "2018"

[dependencies]
tokio = { version = "1.7", features = ["full"] }

sleepless/src/main.rs

use tokio::join;
use std::time::Duration;

async fn count_and_wait(n: u64) -> u64 {
    println!("Starting {}", n);
    std::thread::sleep(Duration::from_millis(n * 100));
    println!("Returning {}", n);
    n
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Join runs multiple tasks concurrently and returns when they all
    // complete execution.
    join!(count_and_wait(1), count_and_wait(2), count_and_wait(3));
    Ok(())
}

Guess the ...