如何在多线程应用程序中使用VecDeque？

Question

如何在多线程应用程序中使用VecDeque？

我正在尝试使用VecDeque. 我想将它用作对所有线程具有读写权限的共享队列。我有以下代码：

use std::collections::VecDeque;
use std::{thread, time};

fn main() {
    let mut workload = VecDeque::new();
    workload.push_back(0);

    let mut thread_1_queue = workload.clone();
    let thread_1 = thread::spawn(move || {
        let mut counter1: i32 = 0;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter1 +=1;
            thread_1_queue.push_back(counter1);

            println!("Thread #1: {:?}", thread_1_queue);

            if counter1 == 10 {
                break;
            }

            thread::sleep(some_time);
        };
    });

    let mut thread_2_queue = workload.clone();
    let thread_2 = thread::spawn(move || {
        let mut counter2: i32 = 10;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter2 +=1;
            thread_2_queue.push_back(counter2);

            println!("Thread #2: {:?}", thread_2_queue);

            if counter2 == 20 {
                break;
            }

            thread::sleep(some_time);
        };
    });

    let some_time = time::Duration::from_millis(50);

    loop {
        if workload.capacity() == 10 {
            break;
        }

        println!("MainQueue: {:?}", workload);

        thread::sleep(some_time);
    }

    thread_1.join();
    thread_2.join();
}

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我现在的问题是线程中的克隆不会更新主队列。现在每个线程都有自己的队列，而不是共享一个。如图所示：

use std::collections::VecDeque;
use std::{thread, time};

fn main() {
    let mut workload = VecDeque::new();
    workload.push_back(0);

    let mut thread_1_queue = workload.clone();
    let thread_1 = thread::spawn(move || {
        let mut counter1: i32 = 0;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter1 +=1;
            thread_1_queue.push_back(counter1);

            println!("Thread #1: {:?}", thread_1_queue);

            if counter1 == 10 {
                break;
            }

            thread::sleep(some_time);
        };
    });

    let mut thread_2_queue = workload.clone();
    let thread_2 = thread::spawn(move || {
        let mut counter2: i32 = 10;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter2 +=1;
            thread_2_queue.push_back(counter2);

            println!("Thread #2: {:?}", thread_2_queue);

            if counter2 == 20 {
                break;
            }

            thread::sleep(some_time);
        };
    });

    let some_time = time::Duration::from_millis(50);

    loop {
        if workload.capacity() == 10 {
            break;
        }

        println!("MainQueue: {:?}", workload);

        thread::sleep(some_time);
    }

    thread_1.join();
    thread_2.join();
}

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Answer 1

Fin*_*nis 5

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

fn main() {
    let workload = Arc::new(Mutex::new(VecDeque::new()));
    workload.lock().unwrap().push_back(0);

    let thread_1_queue = workload.clone();
    let thread_1 = thread::spawn(move || {
        let mut counter1: i32 = 0;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter1 += 1;
            thread_1_queue.lock().unwrap().push_back(counter1);

            println!("Thread #1: {:?}", thread_1_queue.lock().unwrap());

            if counter1 == 10 {
                break;
            }

            thread::sleep(some_time);
        }
    });

    let thread_2_queue = workload.clone();
    let thread_2 = thread::spawn(move || {
        let mut counter2: i32 = 10;
        let some_time = time::Duration::from_millis(50);

        loop {
            counter2 += 1;
            thread_2_queue.lock().unwrap().push_back(counter2);

            println!("Thread #2: {:?}", thread_2_queue.lock().unwrap());

            if counter2 == 20 {
                break;
            }

            thread::sleep(some_time);
        }
    });

    let some_time = time::Duration::from_millis(50);

    loop {
        if workload.lock().unwrap().capacity() == 10 {
            break;
        }

        println!("MainQueue: {:?}", workload.lock().unwrap());

        thread::sleep(some_time);
    }

    thread_1.join();
    thread_2.join();
}

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Thread #1: [0, 1]
MainQueue: [0, 1]
Thread #2: [0, 1, 11]
MainQueue: [0, 1, 11]
Thread #2: [0, 1, 11, 12]
Thread #1: [0, 1, 11, 12, 2]
MainQueue: [0, 1, 11, 12, 2]
Thread #2: [0, 1, 11, 12, 2, 13]
Thread #1: [0, 1, 11, 12, 2, 13, 3]
MainQueue: [0, 1, 11, 12, 2, 13, 3]
Thread #2: [0, 1, 11, 12, 2, 13, 3, 14]
Thread #1: [0, 1, 11, 12, 2, 13, 3, 14, 4]
MainQueue: [0, 1, 11, 12, 2, 13, 3, 14, 4]
Thread #2: [0, 1, 11, 12, 2, 13, 3, 14, 4, 15]
Thread #1: [0, 1, 11, 12, 2, 13, 3, 14, 4, 15, 5]
...

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解释

Arc创建一个多线程引用计数器，您可以使用它向多个线程共享单个对象。请注意，的内容始终Arc是不可变的，因为 Rust 中永远不允许对同一对象进行多个可变引用。

这就是为什么你需要一个Mutex内部的。它创造了所谓的内部可变性。这意味着，您可以使用它临时获得对对象的可变访问，同时确保可变访问不会与其他线程发生冲突。

此外，这意味着当另一个线程在lock()已锁定的情况下调用时，它将阻塞另一个线程。这就是所谓的瓶颈，它将限制您从多线程中获得的加速量。

此外，请注意，在两个lock()s 之间，队列的内容可能会发生变化。因此，如果队列中原子发生的事情很重要，则需要在该操作的整个持续时间内保持队列锁定，这会进一步降低加速速度。

更多错误

我认为你混淆了.capacity()和.len()。

Result您应该使用of做一些事情.join()，我在这里将简单地做一些事情.unwrap()。

.len() == 10在多线程场景中不起作用，因为它可以直接从跳转9到11。所以对于多线程场景，最好这样做>= 10，这总是有效的。

修复了无法永远运行的代码：

Thread #1: [0, 1] MainQueue: [0, 1] Thread #2: [0, 1, 11] MainQueue: [0, 1, 11] Thread #2: [0, 1, 11, 12] Thread #1: [0, 1, 11, 12, 2] MainQueue: [0, 1, 11, 12, 2] Thread #2: [0, 1, 11, 12, 2, 13] Thread #1: [0, 1, 11, 12, 2, 13, 3] MainQueue: [0, 1, 11, 12, 2, 13, 3] Thread #2: [0, 1, 11, 12, 2, 13, 3, 14] Thread #1: [0, 1, 11, 12, 2, 13, 3, 14, 4] MainQueue: [0, 1, 11, 12, 2, 13, 3, 14, 4] Thread #2: [0, 1, 11, 12, 2, 13, 3, 14, 4, 15] Thread #1: [0, 1, 11, 12, 2, 13, 3, 14, 4, 15, 5] ...
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Thread #1: [0, 1] Thread #2: [0, 1, 11] MainQueue: [0, 1, 11] Thread #1: [0, 1, 11, 2] Thread #2: [0, 1, 11, 2, 12] MainQueue: [0, 1, 11, 2, 12] Thread #1: [0, 1, 11, 2, 12, 3] MainQueue: [0, 1, 11, 2, 12, 3] Thread #2: [0, 1, 11, 2, 12, 3, 13] MainQueue: [0, 1, 11, 2, 12, 3, 13] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4] MainQueue: [0, 1, 11, 2, 12, 3, 13, 14, 4] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18, 8] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18, 8, 19] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18, 8, 19, 9] Thread #2: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18, 8, 19, 9, 20] Thread #1: [0, 1, 11, 2, 12, 3, 13, 14, 4, 15, 5, 16, 6, 17, 7, 18, 8, 19, 9, 20, 10]
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