random.rs

use std::io;
use std::io::Read;
use std::sync::Once;
use std::os::unix::io::{RawFd, AsRawFd, FromRawFd};
use std::time::Instant;
use std::fs::File;

static mut RNG_SOURCE: RawFd = 0;
static RNG_INIT: Once = Once::new();

fn get_fd() -> RawFd {
    unsafe {
        RNG_INIT.call_once(|| {
            let f = File::open("/dev/urandom").unwrap();
            RNG_SOURCE = f.as_raw_fd();
            std::mem::forget(f);
        });
        RNG_SOURCE
    }
}

fn fill(buf: &mut [u8]) -> io::Result<()> {
    unsafe {
        let mut f = File::from_raw_fd(get_fd());
        f.read_exact(buf)?;
        std::mem::forget(f);
    }
    Ok(())
}

fn main() {
    let mut buf = vec![0u8; 1_000_000_000];
    let t0 = Instant::now();

    let handle = std::thread::spawn(move || {
        std::thread::sleep(std::time::Duration::from_millis(100));
        let t1 = Instant::now();
        let mut buf = [0u8; 32];
        fill(&mut buf).unwrap();
        println!("thread 1: {:?} {:?}", t0.elapsed(), t1.elapsed());
    });
    fill(&mut buf).unwrap();

    println!("thread 0: {:?}", t0.elapsed());
    handle.join().unwrap();
}