如何在循环间隔内同时运行一组函数，而不使用 Tokio 同时运行相同的函数？

Question

我的目标是同时运行 N 个函数，但在所有函数都完成之前不想产生更多。这是what I have so far：

extern crate tokio;
extern crate futures;

use futures::future::lazy;
use std::{thread, time};
use tokio::prelude::*;
use tokio::timer::Interval;

fn main() {
    let task = Interval::new(time::Instant::now(), time::Duration::new(1, 0))
        .for_each(|interval| {
            println!("Interval: {:?}", interval);
            for i in 0..5 {
                tokio::spawn(lazy(move || {
                    println!("Hello from task {}", i);
                    // mock delay (something blocking)
                    // thread::sleep(time::Duration::from_secs(3));
                    Command::new("sleep").arg("3").output().expect("failed to execute process");

                    Ok(())
                }));
            }
            Ok(())
        })
    .map_err(|e| panic!("interval errored; err={:?}", e));

    tokio::run(task);
}

我每秒生成 5 个函数，但我现在想等到所有函数都完成后再生成更多函数。

根据我的理解（我可能理解错了），我将在另一个未来返回Future

task (Interval ----------------------+ (outer future)
    for i in 0..5 {                  |
        tokio::spawn(  ----+         | 
            // my function | (inner) |
            Ok(())         |         |
        )              ----+         |
    }                                |
    Ok(()) --------------------------+

我一直在努力等待内心的未来结束。

Answer 1

您可以通过加入您的 worker futures 来实现这一点，这样它们都并行运行，但必须一起完成。然后，出于相同的原因，您可以延迟 1 秒加入。将其包装成一个循环以永远运行它（或 5 次迭代，用于演示）。

东京 1.3

use futures::{future, future::BoxFuture, stream, FutureExt, StreamExt}; // 0.3.13
use std::time::{Duration, Instant};
use tokio::time; // 1.3.0

#[tokio::main]
async fn main() {
    let now = Instant::now();
    let forever = stream::unfold((), |()| async {
        eprintln!("Loop starting at {:?}", Instant::now());

        // Resolves when all pages are done
        let batch_of_pages = future::join_all(all_pages());

        // Resolves when both all pages and a delay of 1 second is done
        future::join(batch_of_pages, time::sleep(Duration::from_secs(1))).await;
        
        Some(((), ()))
    });

    forever.take(5).for_each(|_| async {}).await;
    eprintln!("Took {:?}", now.elapsed());
}

fn all_pages() -> Vec<BoxFuture<'static, ()>> {
    vec![page("a", 100).boxed(), page("b", 200).boxed()]
}

async fn page(name: &'static str, time_ms: u64) {
    eprintln!("page {} starting", name);
    time::sleep(Duration::from_millis(time_ms)).await;
    eprintln!("page {} done", name);
}

Loop starting at Instant { t: 1022680437923626 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { t: 1022681444390534 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { t: 1022682453240399 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { t: 1022683469924126 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { t: 1022684493522592 }
page a starting
page b starting
page a done
page b done
Took 5.057315596s

东京 0.1

use futures::future::{self, Loop}; // 0.1.26
use std::time::{Duration, Instant};
use tokio::{prelude::*, timer::Delay};  // 0.1.18

fn main() {
    let repeat_count = Some(5);

    let forever = future::loop_fn(repeat_count, |repeat_count| {
        eprintln!("Loop starting at {:?}", Instant::now());

        // Resolves when all pages are done
        let batch_of_pages = future::join_all(all_pages());

        // Resolves when both all pages and a delay of 1 second is done
        let wait = Future::join(batch_of_pages, ez_delay_ms(1000));

        // Run all this again
        wait.map(move |_| {
            if let Some(0) = repeat_count {
                Loop::Break(())
            } else {
                Loop::Continue(repeat_count.map(|c| c - 1))
            }
        })
    });

    tokio::run(forever.map_err(drop));
}

fn all_pages() -> Vec<Box<dyn Future<Item = (), Error = ()> + Send + 'static>> {
    vec![Box::new(page("a", 100)), Box::new(page("b", 200))]
}

fn page(name: &'static str, time_ms: u64) -> impl Future<Item = (), Error = ()> + Send + 'static {
    future::ok(())
        .inspect(move |_| eprintln!("page {} starting", name))
        .and_then(move |_| ez_delay_ms(time_ms))
        .inspect(move |_| eprintln!("page {} done", name))
}

fn ez_delay_ms(ms: u64) -> impl Future<Item = (), Error = ()> + Send + 'static {
    Delay::new(Instant::now() + Duration::from_millis(ms)).map_err(drop)
}

Loop starting at Instant { tv_sec: 4031391, tv_nsec: 806352322 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { tv_sec: 4031392, tv_nsec: 807792559 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { tv_sec: 4031393, tv_nsec: 809117958 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { tv_sec: 4031394, tv_nsec: 813142458 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { tv_sec: 4031395, tv_nsec: 814407116 }
page a starting
page b starting
page a done
page b done
Loop starting at Instant { tv_sec: 4031396, tv_nsec: 815342642 }
page a starting
page b starting
page a done
page b done

另见：

• Why does Future::select choose the future with a longer sleep period first?
• What is the best approach to encapsulate blocking I/O in future-rs?
• How do I read the output of a child process without blocking in Rust?

Answer 2

根据我的理解（我可能理解错了），我是 在另一个未来返回Future

您没有错，但在您提供的代码中，唯一返回的未来是 Ok(())，它实现了 IntoFuture。 tokio::spawn 只是将新任务生成到 Tokio 的 DefaultExecutor 中。

如果我从您的问题中理解，您想在 上一个 完成后生成 下一批，但如果上一个在 1 秒之前完成，您想要在产生下一批之前完成那 1 秒。

实现自己的未来并自己处理民意调查将是更好的解决方案，但这可以大致完成：

• 通过join_all收集批处理任务。这是一个等待收集的期货完成的新未来。
• 等待 1 秒 后，您可以使用原子状态。如果它被锁定为刻度，它会等到状态释放。

这里是代码（Playground）：

extern crate futures;
extern crate tokio;

use futures::future::lazy;
use std::time::{self, Duration, Instant};

use tokio::prelude::*;
use tokio::timer::{Delay, Interval};

use futures::future::join_all;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;

fn main() {
    let locker = Arc::new(AtomicBool::new(false));

    let task = Interval::new(time::Instant::now(), time::Duration::new(1, 0))
        .map_err(|e| panic!("interval errored; err={:?}", e))
        .for_each(move |interval| {
            let is_locked = locker.load(Ordering::SeqCst);
            println!("Interval: {:?} --- {:?}", interval, is_locked);

            if !is_locked {
                locker.store(true, Ordering::SeqCst);
                println!("locked");

                let futures: Vec<_> = (0..5)
                    .map(|i| {
                        lazy(move || {
                            println!("Running Task-{}", i);
                            // mock delay
                            Delay::new(Instant::now() + Duration::from_millis(100 - i))
                                .then(|_| Ok(()))
                        })
                        .and_then(move |_| {
                            println!("Task-{} is done", i);
                            Ok(())
                        })
                    })
                    .collect();

                let unlocker = locker.clone();
                tokio::spawn(join_all(futures).and_then(move |_| {
                    unlocker.store(false, Ordering::SeqCst);
                    println!("unlocked");

                    Ok(())
                }));
            }

            Ok(())
        });

    tokio::run(task.then(|_| Ok(())));
}

输出：

Interval: Instant { tv_sec: 4036783, tv_nsec: 211837425 } --- false
locked
Running Task-0
Running Task-1
Running Task-2
Running Task-3
Running Task-4
Task-4 is done
Task-3 is done
Task-2 is done
Task-1 is done
Task-0 is done
unlocked
Interval: Instant { tv_sec: 4036784, tv_nsec: 211837425 } --- false
locked
Running Task-0
Running Task-1
Running Task-2
Running Task-3
Running Task-4
Task-3 is done
Task-4 is done
Task-0 is done
Task-1 is done
Task-2 is done
unlocked

警告！ :请查看Shepmaster's comment

即使是为了演示，you should not use thread:sleep 在期货中。 还有更好的选择