Rustでの非同期処理(async/await)

//
// original from https://qiita.com/Kumassy/items/fec47952d70b5073b1b7
//
// [dependencies]
// tokio = { version = "1.42", features = ["full"] }
use std::{thread, time};
use tokio::time::{sleep, Duration};

async fn hello() -> String {
    let one_sec = time::Duration::from_millis(1000);
    // in case of async application, it looks better to use tokio::time crate
    // delay_for : before tokio 0.2
    sleep(Duration::from_millis(1000)).await;
    thread::sleep(one_sec);

    "hello, async fn".to_string()
}

// tokio: to support async runtime
#[tokio::main]
// the async keyword of the fn main() is necessary
async fn main() {
    // excute sysnc function and wait completion
    let greeting: String = hello().await;
    println!("{}", greeting);

    // new task create(spawn)
    // return the type Result
    // 
    let handle = tokio::spawn(async {
        sleep(Duration::from_millis(1000)).await;
        "spawn thread elapsed one second".to_string()
    });

    // define async block
    //
    let world = async {
        let one_sec = time::Duration::from_millis(1000);
        thread::sleep(one_sec);

        println!("hello, async block");
    };

    // rcv spwan thread return
    let result: String = handle.await.unwrap();
    println!("{}", result);

    // async block call and wait
    world.await;

    // wait to avoid main thread terminate before spawn task complete
    sleep(Duration::from_millis(1500)).await;
}