Struct tokio::sync::semaphore::SemaphorePermit

source ·

pub struct SemaphorePermit<'a> {
    sem: &'a Semaphore,
    permits: u32,
}

Expand description

A permit from the semaphore.

This type is created by the acquire method.

Fields§

§sem: &'a Semaphore§permits: u32

Implementations§

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impl<'a> SemaphorePermit<'a>

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pub fn forget(self)

Forgets the permit without releasing it back to the semaphore. This can be used to reduce the amount of permits available from a semaphore.

§Examples

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);

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pub fn merge(&mut self, other: Self)

Merge two SemaphorePermit instances together, consuming other without releasing the permits it holds.

Permits held by both self and other are released when self drops.

§Panics

This function panics if permits from different Semaphore instances are merged.

§Examples

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);

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pub fn split(&mut self, n: usize) -> Option<Self>

Splits n permits from self and returns a new SemaphorePermit instance that holds n permits.

If there are insufficient permits and it’s not possible to reduce by n, returns None.

§Examples

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);