Question

我学习Rust，我尝试构建一个建立在hyper之上的微路由系统（它仅用于学习目的，我知道框架存在）。

我不知道如何与hyper::server::Handler分享“复杂”类型。我读了错误信息，但不幸的是，我不明白如何解决它（大多数时候，生锈编译器只是说要解决什么，现在我不确定理解）。

这是我尝试过的（非）工作过度简化的例子：

extern crate hyper;
use std::sync::Mutex;

use hyper::*;

type Route = (method::Method, String, Box<Fn(server::Request, server::Response)>);

struct MyHandler {
    routes: Mutex<Vec<Route>>
}

impl server::Handler for MyHandler {
    fn handle(&self, req: server::Request, mut res: server::Response) {
        // This is not important
    }
}

fn main() {
    // This is not important
}

错误是：

error: the trait bound `for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static: std::marker::Send` is not satisfied [--explain E0277]
  --> src/main.rs:12:10
   |>
12 |>     impl server::Handler for MyHandler {
   |>          ^^^^^^^^^^^^^^^
note: `for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static` cannot be sent between threads safely
note: required because it appears within the type `Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>`
note: required because it appears within the type `(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)`
note: required because of the requirements on the impl of `std::marker::Send` for `std::ptr::Unique<(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)>`
note: required because it appears within the type `alloc::raw_vec::RawVec<(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)>`
note: required because it appears within the type `std::vec::Vec<(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)>`
note: required because of the requirements on the impl of `std::marker::Send` for `std::sync::Mutex<std::vec::Vec<(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)>>`
note: required because it appears within the type `MyHandler`
note: required by `hyper::server::Handler`

如果我使用简单整数，但不使用Route类型，则可以使用。

因此，该特性存在问题，并且“无法安全地在线程之间发送”。阅读hyper doc，我添加了Mutex，但我必须愚蠢，我不知道我在做什么，不确定我是否应该停止学习Rust，或继续尝试。

Answer 1

你几乎就在那里。

错误是MyHandler没有实现Send特征，这意味着类型可以安全地发送到其他线程：

note: required because of the requirements on the impl of `std::marker::Send` for `std::sync::Mutex<std::vec::Vec<(hyper::method::Method, std::string::String, Box<for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static>)>>`
note: required because it appears within the type `MyHandler`
note: required by `hyper::server::Handler`

错误确实指向了正确的位置，但它有点压倒性。第一行是：

note: `for<'r, 'r, 'r> std::ops::Fn(hyper::server::Request<'r, 'r>, hyper::server::Response<'r>) + 'static` cannot be sent between threads safely

这表示Fn类型没有实现Send。这是Route类型中的一个：

type Route = (method::Method, String, Box<Fn(server::Request, server::Response)>);

Fn闭包只有Send，如果它捕获的所有变量也是Send，但在这里我们不知道传入的任何闭包是否合适。

解决方案很简单：将Fn类型约束为Send：

type Route = (method::Method, String, Box<Fn(server::Request, server::Response)+Send>);

`for＆lt;'r，'r，'r＆gt; ...`无法安全地在线程之间发送

1 个答案: