Tokio

Tokio provides:

• A multi-threaded runtime for executing asynchronous code.
• An asynchronous version of the standard library.
• A large ecosystem of libraries.

# // Copyright 2024 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use tokio::time;

async fn count_to(count: i32) {
    for i in 0..count {
        println!("Count in task: {i}!");
        time::sleep(time::Duration::from_millis(5)).await;
    }
}

#[tokio::main]
async fn main() {
    tokio::spawn(count_to(10));

    for i in 0..5 {
        println!("Main task: {i}");
        time::sleep(time::Duration::from_millis(5)).await;
    }
}

• With the tokio::main macro we can now make main async.

• The spawn function creates a new, concurrent "task".

• Note: spawn takes a Future, you don't call .await on count_to.

Further exploration:

• Why does count_to not get to 10? This is an example of async cancellation. tokio::spawn returns a handle which can be awaited to wait until it finishes.

• Try count_to(10).await instead of spawning.

• Try awaiting the task returned from tokio::spawn.