Spawning tasks in Rust

tokio::spawn hands a future to the runtime and returns a JoinHandle.

use tokio::time::{sleep, Duration};

async fn work(id: u32) -> u32 {
    sleep(Duration::from_millis(10 * id as u64)).await;
    id * id
}

#[tokio::main]
async fn main() {
    let mut handles = Vec::new();
    for id in 1..=4 {
        handles.push(tokio::spawn(work(id)));
    }

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

How it works

1. Tasks are cheap: thousands per thread is normal.
2. The handle resolves to the task's output.
3. A spawned future must be 'static, so move what it needs.

Keywords and builtins used here

• Vec
• as
• async
• await
• fn
• for
• in
• let
• main
• mut
• u32
• u64
• use
• work

The run, in numbers

Lines

18

Characters to type

320

Tokens

107

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 58 seconds.

Type this snippet

Step 2 of 6 in Async with tokio, step 10 of 15 in Concurrency & async.

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