What is the difference between Condvar and notify_one?

Question

Accepted Answer

**Condvar** — condition variable. **notify_one** — wake one waiter.

**Condvar:**
- Wait for condition.
- Pair with Mutex.
- Manual management.

**notify_one:**
- Wake one waiting thread.
- Used with Condvar.
- Selective wakeup.

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

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

thread::spawn(move || {
    let (lock, cvar) = &*pair2;
    let mut ready = lock.lock().unwrap();
    *ready = true;
    cvar.notify_one();
});

let (lock, cvar) = &*pair;
let mut ready = lock.lock().unwrap();
while !*ready {
    ready = cvar.wait(ready).unwrap();
}
```

**Key:** Condvar for condition waiting, notify_one for selective wakeup.

Rust: What is the difference between Condvar and notify_one?