async-await - 如何在Tokio中使用async/await语法？

我正在尝试对Rust中的进程使用异步/等待。我正在使用tokio和tokio-process:

#![feature(await_macro, async_await, futures_api)]

extern crate tokio;
extern crate tokio_process;

use std::process::Command;
use tokio_process::CommandExt;

fn main() {
    tokio::run_async(main_async());
}

async fn main_async() {
    let out = Command::new("echo")
        .arg("hello")
        .arg("world")
        .output_async();
    let s = await!(out);
}

这是我得到的错误:

error[E0277]: the trait bound `tokio_process::OutputAsync: std::future::Future` is not satisfied
  --> src/main.rs:21:13
   |
21 |     let s = await!(out);
   |             ^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `tokio_process::OutputAsync`
   |
   = note: required by `std::future::poll_with_tls_waker`
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0277]: the trait bound `tokio_process::OutputAsync: std::future::Future` is not satisfied
  --> src/main.rs:21:13
   |
21 |     let s = await!(out);
   |             ^^^^^^^^^^^ the trait `std::future::Future` is not implemented for `tokio_process::OutputAsync`
   |
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

我该如何正确处理？

最佳答案

TL; DR:使用Tokio 0.2或更高版本，它应该可以正常工作。

Tokio 0.1和相关的 crate 是使用 future 0.1 crate 实现的。从概念上讲，此 crate 中的Future特征与标准库中Future特征的版本相似，但细节上却大不相同。 async/await语法是围绕标准库中的特征版本构建的。

使用标准库Future实现了Tokio 0.2和相关的 crate ，并对其进行了重新设计以更好地支持async/await语法。

东京0.2

[dependencies]
tokio = { version = "0.2", features = ["full"] }

use tokio::process::Command;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let out = Command::new("echo")
        .arg("hello")
        .arg("world")
        .output()
        .await?;

    let s = String::from_utf8_lossy(&out.stdout);

    println!("{}", s);
    Ok(())
}

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
     Running `target/debug/tokio2`
hello world

经过测试:

Rustc 1.39.0

东京0.1

您必须translate between a Future implemented against the trait from the futures 0.1 crate and from the standard library。另外，您需要启动Tokio运行时服务，最好同时运行Tokio 0.1和Tokio 0.3。那是tokio-compat出现的地方:

[dependencies]
futures = { version = "0.3", features = ["compat"] }
tokio-compat = "0.1"
tokio-process = "0.2"

use futures::compat::Future01CompatExt;
use std::process::Command;
use tokio_process::CommandExt;

fn main() {
    tokio_compat::run_std(main_async());
}

async fn main_async() {
    let out = Command::new("echo")
        .arg("hello")
        .arg("world")
        .output_async();

    // Convert future from 0.1 to 0.3
    let s = out.compat().await;

    println!("{:?}", s);
}

% cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.07s
     Running `target/debug/tt`
Ok(Output { status: ExitStatus(ExitStatus(0)), stdout: "hello world\n", stderr: "" })

经过Rust 1.43.0测试

也可以看看:

How do I convert an async / standard library future to futures 0.1?

Is there a way that we can convert from futures 0.1 to the standard library futures?

Why is a trait not implemented for a type that clearly has it implemented?

关于async-await - 如何在Tokio中使用async/await语法？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/54853917/