Rust tokio::spawn await

tokio-spawn-await.rs

/*
$ cargo run --release --bin sp1
    Finished release [optimized] target(s) in 0.09s
     Running `target/release/sp1`
9227465
14930352
24157817
39088169
63245986
102334155
165580141
267914296
433494437
701408733
Seq dumb fibonacci took: 10.109140154s
--------------
9227465
14930352
24157817
39088169
63245986
102334155
165580141
267914296
433494437
701408733
Async dumb fibonacci took: 4.008534526s
*/
use std::time::Instant;

async fn async_dumb_fibonacci(n: u32) -> u32 {
    dumb_fibonacci(n)
}

fn dumb_fibonacci(n: u32) -> u32 {
    if n <= 1 {
        return n;
    }
    dumb_fibonacci(n - 2) + dumb_fibonacci(n - 1)
}

const L: u32 = 35;
const R: u32 = 45;

#[tokio::main]
async fn main() {
    let start = Instant::now();
    for i in L..R {
        println!("{}", dumb_fibonacci(i));
    }
    let duration = start.elapsed();
    println!("Seq dumb fibonacci took: {:?}", duration);

    println!("--------------");
    // https://users.rust-lang.org/t/tokio-execute-async-for-loop-concurrently/43702/2
    let start = Instant::now();
    let mut handles = Vec::new();
    for i in L..R {
        let job = tokio::spawn(async_dumb_fibonacci(i));
        handles.push(job);
    }

    for job in handles {
        println!("{}", job.await.unwrap());
    }

    let duration = start.elapsed();
    println!("Async dumb fibonacci took: {:?}", duration);
}