Rust 在线程之间不安全地共享没有互斥量的可变数据

免责声明:可能有很多方法来解决这个问题，这只是其中之一，基于@Caesar的 idea .

这篇文章的两个要点:

• 您可以使用AtomicU32在线程之间共享f32，而不会造成任何性能损失(给定u32已经是原子的体系 struct )
• 你可以用std::thread::scope来避免Arc的开销.

use std::{
    fmt::Debug,
    ops::Range,
    sync::atomic::{AtomicU32, Ordering},
};

struct AtomicF32(AtomicU32);
impl AtomicF32 {
    pub fn new(val: f32) -> Self {
        Self(AtomicU32::new(val.to_bits()))
    }
    pub fn load(&self, order: Ordering) -> f32 {
        f32::from_bits(self.0.load(order))
    }
    pub fn store(&self, val: f32, order: Ordering) {
        self.0.store(val.to_bits(), order)
    }
}
impl Debug for AtomicF32 {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.load(Ordering::Relaxed).fmt(f)
    }
}

fn perform_action(data: &Vec<AtomicF32>, range: Range<usize>) {
    for value_raw in &data[range] {
        let mut value = value_raw.load(Ordering::Relaxed);
        value *= 2.5;
        value_raw.store(value, Ordering::Relaxed);
    }
}

fn main() {
    let data = (1..=10)
        .map(|v| AtomicF32::new(v as f32))
        .collect::<Vec<_>>();

    println!("Before: {:?}", data);

    std::thread::scope(|s| {
        s.spawn(|| perform_action(&data, 0..5));
        s.spawn(|| perform_action(&data, 5..10));
    });

    println!("After: {:?}", data);
}

Before: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0]
After: [2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, 20.0, 22.5, 25.0]

要演示这是多么轻量级，请看here is what this compiles to:

use std::{
    sync::atomic::{AtomicU32, Ordering},
};

pub struct AtomicF32(AtomicU32);
impl AtomicF32 {
    fn load(&self, order: Ordering) -> f32 {
        f32::from_bits(self.0.load(order))
    }
    fn store(&self, val: f32, order: Ordering) {
        self.0.store(val.to_bits(), order)
    }
}

pub fn perform_action(value_raw: &AtomicF32) {
    let mut value = value_raw.load(Ordering::Relaxed);
    value *= 2.5;
    value_raw.store(value, Ordering::Relaxed);
}

.LCPI0_0:
        .long   0x40200000
example::perform_action:
        movss   xmm0, dword ptr [rdi]
        mulss   xmm0, dword ptr [rip + .LCPI0_0]
        movss   dword ptr [rdi], xmm0
        ret

请注意，虽然这包含零个未定义的行为，但避免读-修改-写争用条件仍然是程序员的责任.