mysql - 如何将 mysql::Conn 包含在 lazy_static 宏中？

Question

这段代码:

#[macro_use]
extern crate lazy_static;
extern crate mysql;

use mysql::*;

fn some_fn() {
    lazy_static! {
        static ref CONNECTION: Conn = Conn::new("mysql://root:password@127.0.0.1:3306/mydb?prefer_socket=false").unwrap();
    }
}

生成一条很长的错误信息:

error[E0277]: the trait bound `*mut std::os::raw::c_void: std::marker::Sync` is not satisfied in `winapi::minwinbase::OVERLAPPED`
  --> src\main.rs:8:5
   |
8  | /     lazy_static! {
9  | |         static ref CONNECTION: Conn = Conn::new("mysql://root:password@127.0.0.1:3306/mydb?prefer_socket=false").unwrap();
10 | |     }
   | |_____^ `*mut std::os::raw::c_void` cannot be shared between threads safely
   |
   = help: within `winapi::minwinbase::OVERLAPPED`, the trait `std::marker::Sync` is not implemented for `*mut std::os::raw::c_void`
   = note: required because it appears within the type `winapi::minwinbase::OVERLAPPED`
   = note: required because of the requirements on the impl of `std::marker::Sync` for `std::ptr::Unique<winapi::minwinbase::OVERLAPPED>`
   = note: required because it appears within the type `std::boxed::Box<winapi::minwinbase::OVERLAPPED>`
   = note: required because it appears within the type `named_pipe::Overlapped`
   = note: required because it appears within the type `named_pipe::PipeClient`
   = note: required because it appears within the type `std::option::Option<named_pipe::PipeClient>`
   = note: required because it appears within the type `std::io::BufWriter<named_pipe::PipeClient>`
   = note: required because it appears within the type `std::option::Option<std::io::BufWriter<named_pipe::PipeClient>>`
   = note: required because it appears within the type `bufstream::InternalBufWriter<named_pipe::PipeClient>`
   = note: required because it appears within the type `std::io::BufReader<bufstream::InternalBufWriter<named_pipe::PipeClient>>`
   = note: required because it appears within the type `bufstream::BufStream<named_pipe::PipeClient>`
   = note: required because it appears within the type `mysql::io::Stream`
   = note: required because it appears within the type `std::option::Option<mysql::io::Stream>`
   = note: required because it appears within the type `mysql::Conn`
   = note: required by `lazy_static::lazy::Lazy`
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

是因为 mysql::Conn 不适合在多线程应用程序中使用吗？如果我的程序不是多线程的并且我使用非线程安全类型，我如何使用 lazy_static？

Answer 1

您的代码在 macOS 上工作得很好...。我相信这是 a bug with the implementation of the MySQL crate ，作者同意了，在不到一天的时间内修复了这个错误。您应该能够只升级 crate 并使用您的原始代码。

---

作为临时解决方法，您可以将 Conn 包装在 Mutex 中:

use mysql::*;
use std::sync::Mutex;

fn some_fn() {
    lazy_static! {
        static ref CONNECTION: Mutex<Conn> = Mutex::new(Conn::new("mysql://root:password@127.0.0.1:3306/mydb?prefer_socket=false").unwrap());
    }
}

if my program is not multithreaded and I use non-thread-safe types?

我总是建议不要使用全局变量，无论是否使用线程。相反，在您的程序顶部创建您的 Conn 并将对它的引用传递到您的所有函数中。