rust异步之asyncawaitfuture

Posted 2022-01-17 rayylee

1. 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

2. 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.

3. futures

使用futures实现并发

use futures::executor::block_on;
use futures::future::join_all, pending, select_all;
use futures::prelude::*;

async fn a(a: i32, b: i32) -> i32 
    a + b


async fn b(a: i32, b: i32) -> i32 
    a - b


async fn c(a: i32, b: i32) -> i32 
    pending().await


fn main() 
    let r = block_on(async 
        println!("", a(1, 2).await);
        println!("", b(1, 2).await);

        async fn foo(i: u32) -> u32 
            i * 10
        

        let futures = vec![foo(1), foo(2), foo(3)];
        let all_finished = join_all(futures).await;
        println!(":?", all_finished);

        // let first_finished = select_all(futures).await;
        // println!(":?", first_finished);

        "block_on result"
    );
    println!("", r)