waitpid vs waitid race condition demo (It's not a good idea for WNOWAIT to race against reaping)

main.rs

use std::io;
use std::process::Command;
use std::thread;

pub fn waitpid(id: u32) -> io::Result<i32> {
    let mut status = 0i32;
    let ret = unsafe { libc::waitpid(id as i32, &mut status, 0) };
    if ret != -1 {
        Ok(status)
    } else {
        Err(io::Error::last_os_error())
    }
}

pub fn wait_without_reaping(id: u32) -> io::Result<()> {
    let ret = unsafe {
        let mut siginfo = std::mem::zeroed();
        libc::waitid(libc::P_PID, id, &mut siginfo, libc::WEXITED | libc::WNOWAIT)
    };
    if ret == 0 {
        Ok(())
    } else {
        Err(io::Error::last_os_error())
    }
}

fn main() {
    let child = Command::new("sleep").arg("0.1").spawn().unwrap();
    let id = child.id();
    let mut handles = Vec::new();
    for i in 0..3 {
        handles.push(thread::spawn(move || {
            eprintln!("waitid {i} {:?}", wait_without_reaping(id));
        }));
    }
    for i in 0..3 {
        handles.push(thread::spawn(move || {
            eprintln!("waitpid {i} {:?}", waitpid(id));
        }));
    }
    for handle in handles {
        handle.join().unwrap();
    }
}