Struct async_lock::Semaphore

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pub struct Semaphore { /* private fields */ }
Expand description

A counter for limiting the number of concurrent operations.

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impl Semaphore

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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);
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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());
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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;
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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();
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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());
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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;
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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();
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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§

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impl Debug for Semaphore

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

Formats the value using the given formatter. Read more

Auto Trait Implementations§

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.