How to use condvar for thread synchronization

Use Condvar with a Mutex to block a thread until a specific condition is met, then wake it up with notify_one or notify_all.

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

let pair = Arc::new((Mutex::new(false), Condvar::new()));
let pair2 = pair.clone();

// Thread 1: Wait for condition
let (lock, cvar) = &*pair;
cvar.wait(lock.lock().unwrap()).unwrap();

// Thread 2: Signal condition
let (lock, cvar) = &*pair2;
*lock.lock().unwrap() = true;
cvar.notify_one();

A condition variable acts like a doorbell for threads. One thread rings the bell (notifies) when work is ready, and other threads sleep until they hear it (wait). This prevents threads from wasting CPU power by constantly checking if they should start working.