如何从Tokio中的非主线程运行异步任务?

问题描述

use std::thread;
use tokio::task; // 0.3.4

#[tokio::main]
async fn main() {
    thread::spawn(|| {
        task::spawn(async {
            println!("123");
        });
    })
    .join();
}

编译时收到警告:

warning: unused `std::result::Result` that must be used
  --> src/main.rs:6:5
   |
6  | /     thread::spawn(|| {
7  | |         task::spawn(async {
8  | |             println!("123");
9  | |         });
10 | |     })
11 | |     .join();
   | |____________^
   |
   = note: `#[warn(unused_must_use)]` on by default
   = note: this `Result` may be an `Err` variant, which should be handled

执行时出现错误:

thread '<unnamed>' panicked at 'must be called from the context of Tokio runtime configured with either `basic_scheduler` or `threaded_scheduler`', src/main.rs:7:9

推荐答案

关键是您需要获得Tokio Handle .这是对 运行时的引用，它允许您从运行时之外生成异步任务.

The key piece is that you need to get a Tokio Handle. This is a reference to a Runtime and it allows you to spawn asynchronous tasks from outside of the runtime.

使用 #[tokio :: main] ，获取 Handle 的最简单方法是通过 Handle :: current 之前产生另一个线程，然后为可能想要的每个线程提供句柄启动异步任务:

When using #[tokio::main], the simplest way to get a Handle is via Handle::current before spawning another thread then give the handle to each thread that might want to start an asynchronous task:

use std::thread;
use tokio::runtime::Handle; // 0.3.4

#[tokio::main]
async fn main() {
    let threads: Vec<_> = (0..3)
        .map(|thread_id| {
            let handle = Handle::current();

            thread::spawn(move || {
                eprintln!("Thread {} started", thread_id);

                for task_id in 0..3 {
                    handle.spawn(async move {
                        eprintln!("Thread {} / Task {}", thread_id, task_id);
                    });
                }

                eprintln!("Thread {} finished", thread_id);
            })
        })
        .collect();

    for t in threads {
        t.join().expect("Thread panicked");
    }
}

您还可以创建 Mutex< Option< Handle>> ，将其初始化为 None ，然后在 tokio :: main 函数的早期将其设置为 Some .然后，您可以获取该全局变量，将其解包，并在需要时克隆 Handle :

You could also create a global, mutable singleton of a Mutex<Option<Handle>>, initialize it to None, then set it to Some early in your tokio::main function. Then, you can grab that global variable, unwrap it, and clone the Handle when you need it:

use once_cell::sync::Lazy; // 1.5.2

static HANDLE: Lazy<Mutex<Option<Handle>>> = Lazy::new(Default::default);

*HANDLE.lock().unwrap() = Some(Handle::current());

let handle = HANDLE.lock().unwrap().as_ref().unwrap().clone();

另请参阅:

• 如何将任务添加到在另一个线程上运行的Tokio事件循环中?
• 如何在稳定的Rust中同步返回在异步Future中计算出的值?
• 如何为Tokio中的CPU密集型工作创建专用的线程池?
• 如何创建全局的可变单例?

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