为什么Mio的投票因用户生成的事件被触发了两次？

Question

下面的代码生成一个由poll返回的“用户事件”

extern crate mio;

use mio::event::Evented;
use mio::{Events, Poll, PollOpt, Ready, Registration, Token};
use std::thread::{sleep, spawn, JoinHandle};
use std::time::{Duration, Instant};

#[derive(Debug)]
struct Output(u32, Duration);

pub struct MioThread {
    registration: Registration,
    handle: JoinHandle<Output>,
}

impl MioThread {
    pub fn new(i: u32) -> MioThread {
        let now = Instant::now();

        let (registration, set_readiness) = Registration::new2();

        let handle = spawn(move || {
            sleep(Duration::from_millis((1000 - (100 * i)) as u64));

            set_readiness.set_readiness(Ready::readable()).unwrap();

            Output(i, now.elapsed())
        });

        MioThread {
            registration: registration,
            handle: handle,
        }
    }

    // manage the thread result
    fn eval_result(self) {
        let out = self.handle.join();
        println!("do whathever you want with: {:?}", out.unwrap());
    }
}

fn main() {
    let poll = Poll::new().unwrap();

    let mut events = Events::with_capacity(16);

    let mut tasks = Vec::new();
    for i in 0..5 {
        let mio_thread = MioThread::new(i);

        mio_thread
            .registration
            .register(&poll, Token(i as usize), Ready::readable(), PollOpt::edge())
            .unwrap();

        tasks.push(Some(mio_thread));
    }

    loop {
        let num_events = poll.poll(&mut events, None).unwrap();
        println!("poll fired: {} events", num_events);
        for event in &events {
            if event.readiness().is_readable() {
                let Token(thread_id) = event.token();

                if let Some(t) = tasks.remove(thread_id) {
                    t.eval_result();
                }

            }
        }
    }
}

产出如下：

poll fired: 1 events
do whathever you want with: Output(4, Duration { secs: 0, nanos: 600967623 })
poll fired: 0 events
poll fired: 1 events
do whathever you want with: Output(3, Duration { secs: 0, nanos: 701035026 })
poll fired: 0 events
poll fired: 1 events
do whathever you want with: Output(2, Duration { secs: 0, nanos: 801089370 })
poll fired: 0 events
poll fired: 1 events
do whathever you want with: Output(1, Duration { secs: 0, nanos: 900890190 })
poll fired: 0 events
poll fired: 1 events
do whathever you want with: Output(0, Duration { secs: 1, nanos: 600076 })
poll fired: 0 events

我开了关于Mio存储库的一个问题。

Answer 1

如评论和确认的这里中所述

删除注册可能会唤醒循环(它确实是这样做的，就像注册一样)，而不会真正触发事件

在大多数情况下，这显然不是一个问题，只是在阅读了文档之后我没有预料到的行为。

fn轮询(&self，events：&mut，timeout: Option) ->结果−等待就绪事件 阻塞当前线程，并等待已在此Poll实例中注册的任何事件句柄的就绪事件。该函数将被阻塞，直到至少接收到一个就绪事件或超时。超时不意味着在收到就绪事件之前投票将被阻止。

在删除Registration时，也确实会唤醒当前线程。