lockholder.rs

use std::{io, mem};
use std::io::Write;

struct LockHolder {
  stdout_ptr: *mut io::Stdout,
  lock_ptr: *mut io::StdoutLock<'static>,
}

impl LockHolder {
  fn new() -> Self {
    unsafe {
      let stdout = Box::into_raw(Box::new(io::stdout()));
      let lock = Box::into_raw(Box::new((*stdout).lock()));
      return Self { stdout_ptr: stdout, lock_ptr: lock };
    }
  }

  fn print(&mut self, s: &str) -> io::Result<()> {
    unsafe {
      (*self.lock_ptr).write(s.as_bytes())?;
      (*self.lock_ptr).flush()?;
      return Ok(());
    }
  }
}

impl Drop for LockHolder {
  fn drop(&mut self) {
    unsafe {
      mem::drop(Box::from_raw(self.lock_ptr));
      mem::drop(Box::from_raw(self.stdout_ptr));
    }
  }
}

fn main() {
  let mut lh = LockHolder::new();
  lh.print("Hello world!\n").unwrap();
}