线程引用需要静态生命周期? [英] Thread references require static lifetime?

问题描述

虽然从直觉上讲，传递给衍生线程的引用需要具有静态生命周期，但我不清楚究竟是什么导致以下代码无法编译:

While it makes sense intuitively that references passed to spawned threads need to have static lifetimes, I'm unclear about what exactly is making the following code not compile:

use std::sync::Arc;
use std::sync::Mutex;

struct M;

fn do_something(m : Arc<Mutex<&M>>) {
    println!("Ha, do nothing!");
}

fn main() {
    let a = M;
    {
        let c : Arc<Mutex<&M>> = Arc::new(Mutex::new(&a));
        for i in 0..2 {
            let c_clone = c.clone();
            ::std::thread::spawn(move || do_something(c_clone));
        }
    }
}

编译这个小程序出现如下错误:

Compiling this small program gives the following error:

$ rustc -o test test.rs
test.rs:13:55: 13:56 error: `a` does not live long enough
test.rs:13         let c : Arc<Mutex<&M>> = Arc::new(Mutex::new(&a));
                                                             ^
note: reference must be valid for the static lifetime...

在我看来，变量 a 将比 c_clone 更有效，这在这种情况下很重要......?希望有人能帮助我了解我错过了什么！

It seems to me that the variable a will out-live c_clone, which is what matters in this case...? Hopefully someone can help me understand what I'm missing!

推荐答案

在本质上，Arc 和 Mutex 包装是多余的:您传递的是对某物的引用在本地堆栈上.当您使用 std::thread::spawn 生成线程时，没有任何东西将生命周期链接在一起；主线程非常自由地结束并释放其中的任何内容——在这种情况下，包括 a——在它产生的任何其他线程甚至开始执行之前；因此，在这种情况下，a 可以在生成的线程执行任何操作时引用已释放的内存，而将 c_clone 保留为悬空指针.这就是为什么一个衍生线程的关闭环境必须是'static.

In its essence, the Arc and Mutex wrapping is superfluous: you are passing a reference to something on the local stack. When you spawn a thread with std::thread::spawn, there is nothing linking the lifetimes together; the main thread is quite at liberty to conclude and free anything in it—in this case, including a—before any other threads it spawns even start executing; thus in this case a could refer to freed memory by the time the spawned thread does anything, leaving c_clone as a dangling pointer. This is why the environment of the closure of a spawned thread must be 'static.

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