这是一个延续如何在 Rust 的闭包内重用外部作用域的值？，为了更好的呈现，开通了新的Q。
// main.rs
// The value will be modified eventually inside `main`
// and a http request should respond with whatever "current" value it holds.
let mut test_for_closure :Arc<RefCell<String>> = Arc::new(RefCell::from("Foo".to_string()));
// ...
// Handler for HTTP requests
// From https://docs.rs/hyper/0.14.8/hyper/service/fn.service_fn.html
let make_svc = make_service_fn(|_conn| async {
Ok::<_, Infallible>(service_fn(|req: Request<Body>| async move {
if req.version() == Version::HTTP_11 {
let foo:String = *test_for_closure.borrow();
Ok(Response::new(Body::from(foo.as_str())))
} else {
Err("not HTTP/1.1, abort connection")
}
}))
});
不幸的是，我得到RefCell<std::string::String> cannot be shared between threads safely:
RefCell 仅适用于单线程。您将需要使用类似但适用于多线程的互斥体。您可以在这里阅读有关互斥体的更多信息：https://doc.rust-lang.org/std/sync/struct.Mutex.html.
下面是将 Arc
use std::sync::{Arc, Mutex};
fn main() {
let mut test: Arc<Mutex<String>> = Arc::new(Mutex::from("Foo".to_string()));
let mut test_for_closure = Arc::clone(&test);
let closure = || async move {
// lock it so it cant be used in other threads
let foo = test_for_closure.lock().unwrap();
println!("{}", foo);
};
}