RUST Ex00 Async-std

Posted 2020-11-23 wr786

RUST Ex00 Async-std

1 使用Async-std

首先来看一个普通的函数：

use std::fs::File;
use std::io::{self, Read};

fn read_file(path: &str) -> io::Result<String> {
    let mut file = File::open(path)?;
    let mut buffer = String::new();
    file.read_to_string(&mut buffer)?;
    Ok(buffer)
}

将这个函数用Async-std改成异步函数只需要改成这样：

use async_std::fs::File;
use async_std::prelude::*;
use async_std::io;

async fn read_file(path: &str) -> io::Result<String> {
    let mut file = File::open(path).await?;
    let mut buffer = String::new();
    file.read_to_string(&mut buffer).await?;
    Ok(buffer)
}

嗯，没错，只要将std替换成async-std，并且在适当的位置加上async或者await即可。

We used async-std internally. We just replaced "std" by "async-std" and added "async" / "await" at the right places. ——Pascal Hertleif

2 浅析Async-std

async

简单来说，在函数前使用async关键词等价于：

use async_std::fs::File;
use async_std::prelude::*;
use async_std::io;

fn read_file(path: &str) -> impl Future<Item=io::Result<String>> {
    let mut file = File::open(path).await?;
    let mut buffer = String::new();
    file.read_to_string(&mut buffer).await?;
    Ok(buffer)
}

.await

如同字面意思，.await标注了需要等待运行完成的地方。

fn main() {
    let data = read_file("./Cargo.toml");
    // futures do nothing unless you '.await' or poll them
}

• Async函数在被调用时生成futures

3 部分要素

• async_std::task
  • task::block_on This blocks the main thread, executes the future and wait for it to come back.
  • task::spawn This runs a background task and then waits for its completion, blocking the main thread.
  • task::spawn_blocking The returned JoinHandle is exactly the same as for a blocking task.
• .race
• .join futures-rs also provides join_all, joining multiple futures
• async_std::sync::channel

4 AsyncRead/Write/Seek

• AsyncRead: Read from a socket, asynchronously
• AsyncWrite: Write to a socket, asynchronously
• AsyncSeek: Write to a socket, asynchronously

例如：

fn read_from_tcp(socket: async_std::net::TcpSocket) {
    // for applications
}

参考

async/.await with async-std by Florian Gilcher