/*
 * cv-rust.rs
 *
 * Alternating thread pattern using a mutex and condition variable in
 * Rust with an Arc as the object of synchronization.
 *
 * % rustc cv-rust.rs
 * % ./cv-rust
 *
 * Geoff Voelker
 * January 2019
 */

use std::thread;
use std::thread::JoinHandle;
use std::sync::{Arc,Condvar,Mutex};

const ITERS: i32 = 10;

fn alternate (lockcv: Arc<(Mutex<bool>, Condvar)>,
              whoami: &'static str) -> JoinHandle<()> {
    thread::spawn (move || {
        let &(ref lock, ref cv) = &*lockcv;
	let mut arc = lock.lock().unwrap();

	for _ in 0..ITERS {
	    println! ("{}", whoami);
            thread::yield_now();  // 'arbitrary' context switch
	    cv.notify_one();
            thread::yield_now();  // 'arbitrary' context switch
	    arc = cv.wait(arc).unwrap();
            thread::yield_now();  // 'arbitrary' context switch
        }

	// wake up whichever thread is still waiting on the cv
	cv.notify_one();
	// the lock is implicitly released when leaving this scope
    })
}

fn main () {
    let lockcv = Arc::new ((Mutex::new(false), Condvar::new()));

    let ping = alternate (lockcv.clone(), "ping");
    let pong = alternate (lockcv.clone(), "pong");

    ping.join().unwrap();
    pong.join().unwrap();
}