Struct SemaphorePermit

use std::sync::Arc;
use tokio::sync::Semaphore;

let sem = Arc::new(Semaphore::new(10));
{
    let permit = sem.try_acquire_many(5).unwrap();
    assert_eq!(sem.available_permits(), 5);
    permit.forget();
}

// Since we forgot the permit, available permits won't go back to its initial value
// even after the permit is dropped.
assert_eq!(sem.available_permits(), 5);

use std::sync::Arc;
use tokio::sync::Semaphore;

let sem = Arc::new(Semaphore::new(10));
let mut permit = sem.try_acquire().unwrap();

for _ in 0..9 {
    let _permit = sem.try_acquire().unwrap();
    // Merge individual permits into a single one.
    permit.merge(_permit)
}

assert_eq!(sem.available_permits(), 0);

// Release all permits in a single batch.
drop(permit);

assert_eq!(sem.available_permits(), 10);

use std::sync::Arc;
use tokio::sync::Semaphore;

let sem = Arc::new(Semaphore::new(3));

let mut p1 = sem.try_acquire_many(3).unwrap();
let p2 = p1.split(1).unwrap();

assert_eq!(p1.num_permits(), 2);
assert_eq!(p2.num_permits(), 1);