Question

我想在任务之间发送一个特质对象，但无法弄清楚它是否可能。它似乎可能不是，因为它们显然不符合Send特性。

以下代码演示了我尝试做的事情：

use std::{
    sync::mpsc::{channel, Receiver, Sender},
    thread,
};

trait Bar {
    fn bar(&self);
}

struct Foo {
    foo: i32,
}

impl Bar for Foo {
    fn bar(&self) {
        println!("foo: {}", self.foo);
    }
}

fn main() {
    let foo = Box::new(Foo { foo: 1 }) as Box<Bar>;

    let (tx, rx): (Sender<Box<Bar>>, Receiver<Box<Bar>>) = channel();

    thread::spawn(move || {
        tx.send(foo).unwrap();
    });

    let sent = rx.recv().unwrap();

    sent.bar();
}

此操作失败，并显示以下消息：

error[E0277]: `std::sync::mpsc::Sender<std::boxed::Box<Bar>>` cannot be shared between threads safely
  --> src/main.rs:25:5
   |
25 |     thread::spawn(|| {
   |     ^^^^^^^^^^^^^ `std::sync::mpsc::Sender<std::boxed::Box<Bar>>` cannot be shared between threads safely
   |
   = help: the trait `std::marker::Sync` is not implemented for `std::sync::mpsc::Sender<std::boxed::Box<Bar>>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::mpsc::Sender<std::boxed::Box<Bar>>`
   = note: required because it appears within the type `[closure@src/main.rs:25:19: 27:6 tx:&std::sync::mpsc::Sender<std::boxed::Box<Bar>>, foo:std::boxed::Box<Bar>]`
   = note: required by `std::thread::spawn`

error[E0277]: the trait bound `Bar: std::marker::Send` is not satisfied
  --> src/main.rs:25:5
   |
25 |     thread::spawn(|| {
   |     ^^^^^^^^^^^^^ `Bar` cannot be sent between threads safely
   |
   = help: the trait `std::marker::Send` is not implemented for `Bar`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::ptr::Unique<Bar>`
   = note: required because it appears within the type `std::boxed::Box<Bar>`
   = note: required because it appears within the type `[closure@src/main.rs:25:19: 27:6 tx:&std::sync::mpsc::Sender<std::boxed::Box<Bar>>, foo:std::boxed::Box<Bar>]`
   = note: required by `std::thread::spawn`

尝试发送一个简单的，未装箱的特征对象会导致一堆其他错误，主要是抱怨没有完成Send + Sized。

我对Rust还是比较陌生的，所以我不确定是否有我想念的东西，但我得到的印象是没有办法说服编译器制作特征对象Send。

如果目前无法进行，目前是否有任何可能允许此项工作的工作？

Answer 1

这是可能的。您可以向特征对象添加Send约束，如下所示：

let foo = Box::new(Foo { foo: 1 }) as Box<Bar + Send>;

let (tx, rx): (Sender<Box<Bar + Send>>, Receiver<Box<Bar + Send>>) = channel();

在Rust中的线程之间发送特征对象

1 个答案: