打印更新值之前应更新

发布于 2025-02-12 13:15:32 字数 1037 浏览 0 评论 0原文

这是一个简短的代码，

use std::{thread, time::{Duration}, sync::{Arc, Mutex}};

fn main() {
    let num = Arc::new(Mutex::new(0u8));
    let clone = num.clone();

    thread::spawn(move || {
        loop {
            println!("{:?};", *num.lock().unwrap()); // always prints 0
            thread::sleep(Duration::from_secs(1));
            *num.lock().unwrap() = 0;
            println!("{:?};", *num.lock().unwrap()); // always prints 0
        }
    });

    listen(clone);
}

fn listen(num: Arc<Mutex<u8>>) {
    rdev::listen(move |event| {
        match event.event_type {
            rdev::EventType::KeyPress(_) => {
                *num.lock().unwrap() += 1;
            },
            _ => {},
        }
    }).unwrap();
}

它应该做的只是计算用户按键盘上的任何键的次数。但是此代码行不通。

我添加了2 println！语句 - 在更新该值之前。我假设在第一个语句中获得了一个实际值，第二个语句在第二个语句中获得了一个。但是由于某种原因，println！打印一个零。

为什么这么做，如何避免它？

如果我不将值重置为零，则该代码确实可以工作。但是我必须这样做。

原文

Here's a short code

use std::{thread, time::{Duration}, sync::{Arc, Mutex}};

fn main() {
    let num = Arc::new(Mutex::new(0u8));
    let clone = num.clone();

    thread::spawn(move || {
        loop {
            println!("{:?};", *num.lock().unwrap()); // always prints 0
            thread::sleep(Duration::from_secs(1));
            *num.lock().unwrap() = 0;
            println!("{:?};", *num.lock().unwrap()); // always prints 0
        }
    });

    listen(clone);
}

fn listen(num: Arc<Mutex<u8>>) {
    rdev::listen(move |event| {
        match event.event_type {
            rdev::EventType::KeyPress(_) => {
                *num.lock().unwrap() += 1;
            },
            _ => {},
        }
    }).unwrap();
}

All it should do is just counting how many times the users pressed any key on a keyboard. But this code is doesn't work.

I added 2 println! statements - before the value is updated and after that. And I assume to get a real value in the first statement and 0 in the second one. But for some reason both println! print a zero.

Why so and how can I avoid it?

The code does work if I don't reset value to a zero. But I have to do it.

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原谅过去的我 2025-02-19 13:15:32

看来您在num读写之间没有时间。因此，它写入num值并立即从中读取。

您可能想添加一个额外的延迟语句：

loop {
    println!("{:?};", *num.lock().unwrap());
    thread::sleep(Duration::from_secs(1));
    *num.lock().unwrap() = 0;
    println!("{:?};", *num.lock().unwrap());
    //this delay will allow the other thread to modify the num before the read happens.
    thread::sleep(Duration::from_secs(1));
}

It seems that you leave no time between the num read and write. So it writes the num value and immediatly read from it.

You probably want to add an extra delay statement:

loop {
    println!("{:?};", *num.lock().unwrap());
    thread::sleep(Duration::from_secs(1));
    *num.lock().unwrap() = 0;
    println!("{:?};", *num.lock().unwrap());
    //this delay will allow the other thread to modify the num before the read happens.
    thread::sleep(Duration::from_secs(1));
}

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