rust - (tokio::spawn)借用的值生命周期不长-参数要求 `sleepy`是借用的 `' static`

Question

此MWE显示tokio::spawn循环中for in的使用。注释的代码sleepy_futures.push(sleepy.sleep_n(2));可以正常工作，但不能运行/轮询异步功能。
基本上，我想同时运行一堆异步函数。我很高兴更改Sleepy的实现或使用其他库/技术。

pub struct Sleepy;
impl Sleepy {
    pub async fn sleep_n(self: &Self, n: u64) -> String {
        sleep(Duration::from_secs(n));
        "test".to_string()
    }
}

#[tokio::main(core_threads = 4)]
async fn main() {
    let sleepy = Sleepy{};

    let mut sleepy_futures = vec::Vec::new();
    for _ in 0..5 {
        // sleepy_futures.push(sleepy.sleep_n(2));
        sleepy_futures.push(tokio::task::spawn(sleepy.sleep_n(2)));
    }

    let results = futures::future::join_all(sleepy_futures).await;
    for result in results {
        println!("{}", result.unwrap())
    }
}

Answer 1

这是修复问题的粗略方法:

use tokio::time::delay_for;

pub struct Sleepy;
impl Sleepy {
    pub async fn sleep_n(n: u64) -> String {
        delay_for(Duration::from_secs(n)).await;
        "test".to_string()
    }
}

现在，它不再 anchor 定到任何特定的Sleepy实例，从而消除了生命周期问题。您会像 Sleepy::sleep_n这样称呼它。
如果需要 &self，则需要做更多的工作:

use std::sync::Arc;
use std::time::Duration;
use std::vec;
use tokio;
use tokio::time::delay_for;

pub struct Sleepy;
impl Sleepy {
    pub async fn sleep_n(&self, n: u64) -> String {
        // Call .await here to delay properly
        delay_for(Duration::from_secs(n)).await;
        "test".to_string()
    }
}

#[tokio::main(core_threads = 4)]
async fn main() {
    env_logger::init();

    let sleepy = Arc::new(Sleepy {});

    let mut sleepy_futures = vec::Vec::new();
    for _ in 0..5 {
        let sleepy = sleepy.clone();

        // Dictate that values are moved into the task instead of 
        // being borrowed and dropped.  
        sleepy_futures.push(tokio::task::spawn(async move {
            sleepy.sleep_n(2).await
        }));
    }

    let results = futures::future::join_all(sleepy_futures).await;
    for result in results {
        println!("{}", result.unwrap())
    }
}

此处 Arc用于包装对象，因为 task可能使用线程，因此 Rc不够。