rust 2 async functions synchronously, but start to continue to execute the code after the first finished and wait for the second function later

I want to run multiple async functions synchronously. I build a simple example for my problem. sleep1 should be executed at the beginning, but its requiered at a later point. sleep2 and sleep_arr should be executed before. Right now the code takes 8 seconds to complete but it should only take 5.

async fn test() -> bool {
    let sleep1 = sleep(5);
    let sleep2 = sleep(1).await;
    let sleep_arr = vec![sleep(2), sleep(2)];
    join_all(sleep_arr).await;
    sleep1.await;
    return true;
}
async fn sleep(sec: u64) -> () {
    use async_std::task;
    task::sleep(std::time::Duration::from_secs(sec)).await; 
}

>Solution :

You can create an async block for the second sequence and then execute the two sequences that need to be executed in parallel using futures::join!:

async fn test() -> bool {
    let sleep1 = sleep(5);
    let task2 = async {
        let sleep2 = sleep(1).await;
        let sleep_arr = vec![sleep(2), sleep(2)];
        futures::future::join_all(sleep_arr).await;
    };
    futures::join!(sleep1, task2);
    return true;
}

async fn sleep(sec: u64) -> () {
    tokio::time::sleep(std::time::Duration::from_secs(sec)).await;
}

#[tokio::main]
async fn main() {
    let instant = std::time::Instant::now();
    test().await;
    dbg!(instant.elapsed());
}

Output:

[src/main.rs:20] instant.elapsed() = 5.001728234s

(I switched to tokio so it works in the playground but it should be the same with async_std.)

Playground