rust - 异步学习 async,await,future

0x01 最简单的异步 async

The most common way to run a Future is to .await it. When .await is called on a Future, it will attempt to run it to completion.
执行 Future的最简单方法就是调用 await

use futures::executor::block_on;

async fn say_hi() {
    println!("nice");
}

fn main() {
    let future = say_hi();
    // block the current thread until provided future
    block_on(future);
}

使用async 来修饰一个方法, 表示此方法是一个异步任务, 然后在主线程里使用一个执行器宏 block_on 来等待运行结果

0x02 关键字 await

async fn lear_song() {
    println!("learn song");
}

async fn sing_song() {
    println!("sing song");
}

async fn dance() {
    println!("learn dance");
}

async fn learn_and_sing() {
    // study song, and wait
    let song = lear_song().await;
    // then sing song
    sing_song().await;
}

async fn async_main(){
    let f1 = learn_and_sing();
    let f2 = dance();
    futures::join!(f1,f2);
}

fn main() {
    block_on(async_main());
    println!("done");
}

1. 在一个async方法中, 可以执行其他异步任务. 但如果需要顺序执行这些异步任务时, 就需要在上一个任务的后面,执行await方法.
2. 如果想实现barrier类似的效果, 可以通过 futures::join 方法来实现.

0x2.1 展示一下在actix-web的方法中, 返回一个http请求的示例

[dependencies]
actix-web = "2.0"
actix-rt = "1.0"

reqwest = { version = "0.10", features = ["json"] }
tokio = { version = "0.2", features = ["full"] }


use actix_web::{Responder, HttpResponse, HttpServer, web, App};

async fn index() -> impl Responder {
    let resp = reqwest::get("https://httpbin.org/ip").await;
    if let Ok(rsp) = resp {
        let body = rsp.text().await.unwrap();
        HttpResponse::Ok().body(body)
    }
    else {
        HttpResponse::Ok().body("no content!")
    }
}

#[actix_rt::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| {
        App::new()
            .route("/", web::get().to(index))
    })
        .bind("127.0.0.1:8088")?
        .run()
        .await
}