Stdin::lock 在什么情况下有用？

Question

Stdin::lock:

pub fn lock(&self) -> StdinLock<'_>

这在什么情况下有用？

Answer 1

文件指出，我的重点是：

进程的标准输入流的句柄。

每个句柄都是对此进程的输入数据的全局缓冲区的共享引用。可以使用句柄lock来获得对BufRead方法的完全访问权限（例如，.lines()）。否则，对该句柄的读取将相对于其他读取被锁定。

use std::io::{self, prelude::*};

fn main() {
    let stdin = io::stdin();
    
    dbg!(stdin.lines().count()); // fails!
    
    let stdin = stdin.lock();
    dbg!(stdin.lines().count());
}

error[E0599]: no method named `lines` found for struct `std::io::Stdin` in the current scope
   --> src/main.rs:6:16
    |
6   |       dbg!(stdin.lines().count());
    |                  ^^^^^ method not found in `std::io::Stdin`
    |
    = note: the method `lines` exists but the following trait bounds were not satisfied:
            `std::io::Stdin: std::io::BufRead`
            which is required by `&mut std::io::Stdin: std::io::BufRead`