Struct Semaphore

pub struct Semaphore { /* private fields */ }

A counter for limiting the number of concurrent operations.

Implementations

impl Semaphore

pub const fn new(n: usize) -> Semaphore

Creates a new semaphore with a limit of n concurrent operations.

Examples

use async_lock::Semaphore;

let s = Semaphore::new(5);

pub fn try_acquire(&self) -> Option<SemaphoreGuard<'_>>

Attempts to get a permit for a concurrent operation.

If the permit could not be acquired at this time, then None is returned. Otherwise, a guard is returned that releases the mutex when dropped.

Examples

use async_lock::Semaphore;

let s = Semaphore::new(2);

let g1 = s.try_acquire().unwrap();
let g2 = s.try_acquire().unwrap();

assert!(s.try_acquire().is_none());
drop(g2);
assert!(s.try_acquire().is_some());

pub fn acquire(&self) -> Acquire<'_>

Waits for a permit for a concurrent operation.

Returns a guard that releases the permit when dropped.

Examples

use async_lock::Semaphore;

let s = Semaphore::new(2);
let guard = s.acquire().await;

pub fn acquire_blocking(&self) -> SemaphoreGuard<'_>

Waits for a permit for a concurrent operation.

Returns a guard that releases the permit when dropped.

Blocking

Rather than using asynchronous waiting, like the acquire method, this method will block the current thread until the permit is acquired.

This method should not be used in an asynchronous context. It is intended to be used in a way that a semaphore can be used in both asynchronous and synchronous contexts. Calling this method in an asynchronous context may result in a deadlock.

Examples

use async_lock::Semaphore;

let s = Semaphore::new(2);
let guard = s.acquire_blocking();

pub fn try_acquire_arc(self: &Arc<Self>) -> Option<SemaphoreGuardArc>

Attempts to get an owned permit for a concurrent operation.

If the permit could not be acquired at this time, then None is returned. Otherwise, an owned guard is returned that releases the mutex when dropped.

Examples

use async_lock::Semaphore;
use std::sync::Arc;

let s = Arc::new(Semaphore::new(2));

let g1 = s.try_acquire_arc().unwrap();
let g2 = s.try_acquire_arc().unwrap();

assert!(s.try_acquire_arc().is_none());
drop(g2);
assert!(s.try_acquire_arc().is_some());

pub fn acquire_arc(self: &Arc<Self>) -> AcquireArc

Waits for an owned permit for a concurrent operation.

Returns a guard that releases the permit when dropped.

Examples

use async_lock::Semaphore;
use std::sync::Arc;

let s = Arc::new(Semaphore::new(2));
let guard = s.acquire_arc().await;

pub fn acquire_arc_blocking(self: &Arc<Self>) -> SemaphoreGuardArc

Waits for an owned permit for a concurrent operation.

Returns a guard that releases the permit when dropped.

Blocking

Rather than using asynchronous waiting, like the acquire_arc method, this method will block the current thread until the permit is acquired.

This method should not be used in an asynchronous context. It is intended to be used in a way that a semaphore can be used in both asynchronous and synchronous contexts. Calling this method in an asynchronous context may result in a deadlock.

Examples

use std::sync::Arc;
use async_lock::Semaphore;

let s = Arc::new(Semaphore::new(2));
let guard = s.acquire_arc_blocking();

pub fn add_permits(&self, n: usize)

Adds n additional permits to the semaphore.

Examples

use async_lock::Semaphore;

let s = Semaphore::new(1);

let _guard = s.acquire().await;
assert!(s.try_acquire().is_none());

s.add_permits(2);

let _guard = s.acquire().await;
let _guard = s.acquire().await;

Trait Implementations

impl Debug for Semaphore

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.