Rust并发控制之Condvar-两线程交替打印

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

fn main() {
    let pair = Arc::new((Mutex::new(false), Condvar::new()));
    let cnt = 3;
    let pair2 = pair.clone();

    let t1 = thread::spawn(move || {
        let &(ref lock, ref cvar) = &*pair2;
        for _ in 0..cnt {
            while let Ok(mut v) = lock.lock() {
                // 条件为false时开始打印1
                // 并修改条件为true, 通知等待的另一个线程打印2
                if !*v {
                    print!("1 ");
                    *v = true;
                    cvar.notify_one();
                    break;
                } else {
                    // 及时释放锁，不让mutexguard被scope结束时才释放
                    // 如果后续没操作的话，可以不用这里drop，等离开scope时自动释放也一样
                    drop(v);
                    // [2]
                    // std::thread::sleep(std::time::Duration::from_millis(1));
                    // [1]
                    // print!(" waitting... ");
                }
            }
        }
    });
    let t2 = thread::spawn(move || {
        for _ in 0..cnt {
            let &(ref lock, ref cvar) = &*pair;
            let mut v = lock.lock().unwrap();
            // 条件为false时等待notify，直到条件为true
            while !*v {
                v = cvar.wait(v).unwrap();
            }
            // 重置条件为false，并打印2
            *v = false;
            print!("2 ");
        }
    });
    t1.join().unwrap();
    t2.join().unwrap();
}