// /std/src/io/stdio.rs

pub struct StdinLock<'a> {
    inner: MutexGuard<'a, BufReader<StdinRaw>>,
}

impl Stdin {

    pub fn lock(&self) -> StdinLock<'static> {
        // Locks this handle with 'static lifetime. This depends on the
        // implementation detail that the underlying `Mutex` is static.
        StdinLock { inner: self.inner.lock().unwrap_or_else(|e| e.into_inner()) }
    }

}

Since we only have one stdin instance in a process, why does not Stdin::lock just return a owned StdinLock with MutexGuard<'static, ...> instead?