多线程应用程序无法通过错误链进行编译 [英] Multithreaded application fails to compile with error-chain

问题描述

我将error-chain引入了以前可以运行的应用程序中.错误本身很明显，std::error::Error + 'static缺少trait std::marker::Send的实现:

I introduced error-chain into a previously working application. The error itself is clear, std::error::Error + 'static lacks an implementation of the trait std::marker::Send:

error[E0277]: the trait bound `std::error::Error + 'static: std::marker::Send` is not satisfied
  --> src/main.rs:35:5
   |
35 | /     error_chain!{
36 | |
37 | |         foreign_links {
38 | |             Mqttc(::mqttc::Error);
...  |
53 | |         }
54 | |     }
   | |_____^ `std::error::Error + 'static` cannot be sent between threads safely
   |
   = help: the trait `std::marker::Send` is not implemented for `std::error::Error + 'static`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::ptr::Unique<std::error::Error + 'static>`
   = note: required because it appears within the type `std::boxed::Box<std::error::Error + 'static>`
   = note: required because it appears within the type `mqttc::netopt::Error`
   = note: required because it appears within the type `mqttc::Error`
   = note: required because it appears within the type `errors::ErrorKind`
   = note: required because it appears within the type `errors::Error`
   = note: required by `error_chain::ChainedError`
   = note: this error originates in a macro outside of the current crate

我不确定该如何解决.请注意，我正在使用更多的最新的mqttc/mqtt3 分支，而不是上游的板条箱

I am not sure how to resolve this. Note that I am using the more up to date fork of mqttc/mqtt3 instead of the upstream crates.

推荐答案

mqttc::Error包含一个mqttc::netopt::Error，它依次包含一个Box<std::error::Error>(对std::boxed::Box<std::error::Error + 'static>无效).std::error::Error这里是一个特征对象.因为Error特征没有Send作为超特征，所以不需要Error的实现来实现Send.因此，Box<std::error::Error>不能实现Send，因为不是所有类型的实施Send.

mqttc::Error contains a mqttc::netopt::Error, which in turns contains a Box<std::error::Error> (which desugars to std::boxed::Box<std::error::Error + 'static>. std::error::Error here is a trait object. Because the Error trait doesn't have Send as a supertrait, implementations of Error are not required to implement Send. Therefore, Box<std::error::Error> doesn't implement Send because not all types T: std::error::Error implement Send.

这可以通过将mqttc::netopt::Error类型更改为使用Box<std::error::Error + Send>而不是Box<std::error::Error>来解决(这对于库来说是一个重大更改).

This could be fixed by changing the mqttc::netopt::Error type to use Box<std::error::Error + Send> instead of Box<std::error::Error> (which would be a breaking change for the library).

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