Thread_Local！在Rust中使用动态库？

Question

正如标题所示，我对共享库如何与Rust中的线程局部变量一起工作感到困惑。下面我有一个最小的例子：

[package]
name = "minimal_thread_local_example"
version = "0.1.0"
edition = "2018"


[dependencies]
has_thread_local = {path ="./has_thread_local"}
libloading = "0.5"


[workspace]
members = ["shared_library","has_thread_local"]

extern crate libloading;


use libloading::{Library, Symbol};
use has_thread_local::{set_thread_local, get_thread_local};

fn main() {
    let lib = Library::new("libshared_library.so").unwrap();
    set_thread_local(10);
    unsafe {
        let func: Symbol<unsafe extern fn() -> u32> = lib.get(b"print_local").unwrap();
        func();
    };
    println!("From static executable:{}", get_thread_local());
}

在名为has_thread_local的板条箱中：

cargo.toml：

[package]
name = "has_thread_local"
version = "0.1.0"
edition = "2018"

[lib]

[dependencies]

src/lib.rs：

use std::cell::RefCell;
use std::ops::Deref;


thread_local! {
    pub static A_THREAD_LOCAL : RefCell<u64> =  RefCell::new(0);
}

pub fn set_thread_local(val: u64) {
    A_THREAD_LOCAL.with(|refcell| { refcell.replace(val); })
}

pub fn get_thread_local() -> u64 {
    A_THREAD_LOCAL.with(|refcell| *refcell.borrow().deref())
}

[package]
name = "shared-library"
version = "0.1.0"
edition = "2018"

[lib]
crate-type = ["cdylib"]


[dependencies]
has_thread_local = {path = "../has_thread_local"}

use has_thread_local::get_thread_local;

#[no_mangle]
unsafe extern "system" fn print_local() {
    println!("From shared library:{}",get_thread_local());
}

From shared library:0
From static executable:10

Answer 1

之所以观察到这种行为，是因为共享库包含它自己的所依赖的板条箱代码副本，从而导致两个不同的线程本地声明。

解决这个问题的方法是传递对有问题的线程本地的引用，而不是直接访问线程本地。有关如何获取对线程局部变量的引用的更多信息，请参见此处：如何在Rust结构中创建线程局部变量？