pex 0.2.4

A nightly parser combinator library for Rust.
Documentation 
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use std::{
    mem::MaybeUninit,
    sync::{Mutex, Once},
    thread,
    time::Duration,
};

struct SingletonReader {
    // Since we will be used in many threads, we need to protect
    // concurrent access
    inner: Mutex<u8>,
}

fn singleton() -> &'static SingletonReader {
    // Create an uninitialized static
    static mut SINGLETON: MaybeUninit<SingletonReader> = MaybeUninit::uninit();
    static ONCE: Once = Once::new();

    unsafe {
        ONCE.call_once(|| {
            // Make it
            let singleton = SingletonReader { inner: Mutex::new(0) };
            // Store it to the static var, i.e. initialize it
            SINGLETON.write(singleton);
        });

        // Now we give out a shared reference to the data, which is safe to use
        // concurrently.
        SINGLETON.assume_init_ref()
    }
}

fn main() {
    // Let's use the singleton in a few threads
    let threads: Vec<_> = (0..10)
        .map(|i| {
            thread::spawn(move || {
                thread::sleep(Duration::from_millis(i * 10));
                let s = singleton();
                let mut data = s.inner.lock().unwrap();
                *data = i as u8;
            })
        })
        .collect();

    // And let's check the singleton every so often
    for _ in 0u8..20 {
        thread::sleep(Duration::from_millis(5));

        let s = singleton();
        let data = s.inner.lock().unwrap();
        println!("It is: {}", *data);
    }

    for thread in threads.into_iter() {
        thread.join().unwrap();
    }
}