如何在一个线程中更新并从多个线程中读取？

Question

我没能通过借用检查器获取此代码：

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

#[derive(Debug, Clone)]
struct State {
    count: u64,
    not_copyable: Vec<u8>,
}

fn bar(thread_num: u8, arc_state: Arc<State>) {
    let state = arc_state.clone();
    loop {
        sleep(Duration::from_millis(1000));
        println!("thread_num: {}, state.count: {}", thread_num, state.count);
    }
}

fn main() -> std::io::Result<()> {
    let mut state = State {
        count: 0,
        not_copyable: vec![],
    };
    let arc_state = Arc::new(state);

    for i in 0..2 {
        spawn(move || {
            bar(i, arc_state.clone());
        });
    }

    loop {
        sleep(Duration::from_millis(300));
        state.count += 1;
    }
}

我可能试错了。

我想要一个可以更新 state 的（主）线程和多个可以读取 state.

的线程

我应该如何在 Rust 中执行此操作？

我读过 the Rust book on shared state，但它使用的互斥量对于单个编写器/多个 reader 情况来说似乎过于复杂。

在 C 中，我会通过大量 _Atomic.

来实现这一点

Answer 1

Atomics 确实是一种正确的方法，std 中有很多这样的方法（link。您的示例需要 2 个修复。

在进入闭包之前必须克隆 Arc ，因此您的循环变为：

for i in 0..2 { let arc_state = arc_state.clone(); spawn(move || { bar(i, arc_state); }); }

使用 AtomicU64 相当简单，但您需要明确使用具有指定 Ordering (Playground) 的新类型方法):

use std::sync::atomic::{AtomicU64, Ordering}; use std::sync::Arc; use std::thread::{sleep, spawn}; use std::time::Duration; #[derive(Debug)] struct State { count: AtomicU64, not_copyable: Vec<u8>, } fn bar(thread_num: u8, arc_state: Arc<State>) { let state = arc_state.clone(); loop { sleep(Duration::from_millis(1000)); println!( "thread_num: {}, state.count: {}", thread_num, state.count.load(Ordering::Relaxed) ); } } fn main() -> std::io::Result<()> { let state = State { count: AtomicU64::new(0), not_copyable: vec![], }; let arc_state = Arc::new(state); for i in 0..2 { let arc_state = arc_state.clone(); spawn(move || { bar(i, arc_state); }); } loop { sleep(Duration::from_millis(300)); // you can't use `state` here, because it moved arc_state.count.fetch_add(1, Ordering::Relaxed); } }

如何在一个线程中更新并从多个线程中读取？

How to update in one thread and read from many?

multithreading

rust

borrow-checker